[Unified Search] Flip newDateRangePickerEnabled feature flag fallback to true (elastic#264743)

## Summary

This makes the new time picker the default in Discover and Dashboards.

It flips the fallback of the `unifiedSearch.newDateRangePickerEnabled`
feature flag to `true`, so the new `DateRangePicker` becomes the default
when the flag isn't explicitly configured.

See elastic#260163 

To opt back into the legacy `EuiSuperDatePicker` locally, you can
override the flag in `config/kibana.dev.yml`:

```yaml
feature_flags.overrides:
  unifiedSearch.newDateRangePickerEnabled: false
```

## Changes

Follow-up commits on this branch also fix FTR/snapshot fallout from the
flip:

- `_esql_view.ts` (stateful + serverless): replaced hard-coded
`superDatePickerToggleQuickMenuButton` checks with
`timePicker.timePickerExists()` (both picker paths). Specs already had
`// TODO`s for exactly this change.
- `dashboard_controls` light/dark snapshots: regenerated baselines to
reflect the new picker's duration badge on dashboards.
- `ccs_compatibility/_cancel_results.ts` (ES|QL subtest): made the query
submit explicit so it no longer depends on the legacy picker's internal
`querySubmitButton` click.

> [!NOTE]
> Two Flaky Test Runner passes on the affected CCS config are linked in
the comments below.

### Checklist

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Users who have not explicitly set the flag will now see the new
DateRangePicker in place of the legacy `EuiSuperDatePicker`. This is the
entire point of the flag — a staged rollout — so the risk is limited to
UX differences between the two pickers (e.g. the new picker's duration
badge, which required snapshot baseline updates here).

- [ ] ~~[See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)~~

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: acstll

src/platform/plugins/shared/unified_search/public/query_string_input/query_bar_top_row.tsx

@@ -72,7 +72,7 @@ import { shallowEqual } from '../utils/shallow_equal';
 import { FilterBarToggleButton } from '../filter_bar/filter_bar_toggle_button';
 import { FilterBarContextProvider } from '../filter_bar/filter_bar_context';
 
-/** Feature flag key for the new DateRangePicker. Falls back to `false` (legacy picker). */
+/** Feature flag key for the new DateRangePicker. Falls back to `true` (new picker). */
 const DATE_RANGE_PICKER_FEATURE_FLAG = 'unifiedSearch.newDateRangePickerEnabled';
 
 const BUTTON_MIN_WIDTH = 108;
@@ -392,7 +392,7 @@ export const QueryBarTopRow = React.memo(
 
     const shouldUseLegacyTimePicker =
       !props.enableDateRangePicker ||
-      !kibana.services.featureFlags?.getBooleanValue(DATE_RANGE_PICKER_FEATURE_FLAG, false);
+      !kibana.services.featureFlags?.getBooleanValue(DATE_RANGE_PICKER_FEATURE_FLAG, true);
 
     const isQueryLangSelected = props.query && !isOfQueryType(props.query);
     const shouldRenderESQLUi = Boolean(showQueryInput && isQueryLangSelected);

src/platform/test/functional/apps/discover/ccs_compatibility/_cancel_results.ts

@@ -120,10 +120,11 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       it('should show warning and results', async () => {
         await common.navigateToApp('discover');
         await discover.selectTextBaseLang();
+        await timePicker.setDefaultAbsoluteRange();
         await monacoEditor.setCodeEditorValue(`FROM logstash-*, ftr-remote:logstash-* METADATA _index
   | EVAL buckets = DATE_TRUNC(5 minute, @timestamp), delay = TO_STRING(CASE(STARTS_WITH(_index, "ftr-remote"), DELAY(10ms), false))
   | STATS count = COUNT(*) BY buckets, delay`);
-        await timePicker.setDefaultAbsoluteRange();
+        await testSubjects.click('querySubmitButton');
 
         // Wait for the async search to be established on ES so that cancellation can retrieve
         // partial results via the async search ID

src/platform/test/functional/apps/discover/esql_2/_esql_view.ts

@@ -99,8 +99,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         await unifiedFieldList.waitUntilSidebarHasLoaded();
 
         expect(await testSubjects.exists('showQueryBarMenu')).to.be(true);
-        // TODO: use timePicker page object instead of hard-coding test subjects (handles both old and new picker)
-        expect(await testSubjects.exists('superDatePickerToggleQuickMenuButton')).to.be(true);
+        expect(await timePicker.timePickerExists()).to.be(true);
         expect(await testSubjects.exists('addFilter')).to.be(true);
         expect(await testSubjects.exists('dscViewModeDocumentButton')).to.be(true);
         expect(await testSubjects.exists('unifiedHistogramChart')).to.be(true);
@@ -122,8 +121,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
 
         expect(await testSubjects.exists('fieldListFiltersFieldSearch')).to.be(true);
         expect(await testSubjects.exists('ESQLEditor')).to.be(true);
-        // TODO: use timePicker page object instead of hard-coding test subjects (handles both old and new picker)
-        expect(await testSubjects.exists('superDatePickerToggleQuickMenuButton')).to.be(true);
+        expect(await timePicker.timePickerExists()).to.be(true);
 
         expect(await testSubjects.exists('showQueryBarMenu')).to.be(false);
         expect(await testSubjects.exists('addFilter')).to.be(false);

src/platform/test/functional/screenshots/baseline/dashboard_controls_dark.png

@@ -82,8 +82,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         await PageObjects.unifiedFieldList.waitUntilSidebarHasLoaded();
 
         await testSubjects.existOrFail('showQueryBarMenu');
-        // TODO: use timePicker page object instead of hard-coding test subjects (handles both old and new picker)
-        await testSubjects.existOrFail('superDatePickerToggleQuickMenuButton');
+        expect(await PageObjects.timePicker.timePickerExists()).to.be(true);
         await testSubjects.existOrFail('addFilter');
         await testSubjects.existOrFail('dscViewModeDocumentButton');
         await testSubjects.existOrFail('unifiedHistogramChart');
@@ -105,8 +104,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
 
         await testSubjects.existOrFail('fieldListFiltersFieldSearch');
         await testSubjects.existOrFail('ESQLEditor');
-        // TODO: use timePicker page object instead of hard-coding test subjects (handles both old and new picker)
-        await testSubjects.existOrFail('superDatePickerToggleQuickMenuButton');
+        expect(await PageObjects.timePicker.timePickerExists()).to.be(true);
 
         await testSubjects.missingOrFail('showQueryBarMenu');
         await testSubjects.missingOrFail('addFilter');