Closes #254889

Summary

• Introduce a shared VisualizationDatasourceDefaults port in @kbn/lens-common so Lens visualizations can declare datasource-level defaults alongside their dimension groups.
• Use that port to default date histogram includeEmptyRows off for new Bar, Heatmap, Pie, Treemap, Metric, Tag cloud, Waffle, and Mosaic charts, while keeping Datatable defaults on and preserving explicit saved/API values.
• Apply the same defaults consistently across Lens editor flows, subtype switches, chart switches, suggestions, suggestions API subtype selection, and embeddable config-builder/API ingress.

What changed

• Added shared helpers in @kbn/lens-common to:
  • resolve visualization-specific datasource defaults from visualization type/subtype/state
  • apply those defaults when creating column params
  • normalize existing datasource state when a caller needs an explicit chart-specific override
• Added XY and partition chart-family helpers so Bar-family XY subtypes and supported partition shapes share a single source of truth for includeEmptyRows defaults.
• Extended VisualizationDimensionGroupConfig with datasourceDefaults so visualizations can pass datasource defaults directly to the dimension editor instead of routing them through ad hoc editor props.
• Wired datasource defaults into Datatable, Heatmap, Metric, Tag cloud, Partition, and XY visualization configs, including Metric trendline groups.
• Updated form-based datasource column creation/replacement to backfill visualization defaults when building or replacing bucket dimensions.
• Updated chart switch and suggestion flows to normalize datasource state with overwriteExisting: true when the user switches to a chart or subtype whose default should take precedence.
• Updated XY subtype switching so changing a layer between Bar/Line/Area updates both visualization state and the underlying datasource state for the selected layer.
• Updated Lens suggestions API subtype selection to reapply datasource defaults after switchVisualizationType.
• Updated the embeddable config builder and API transforms so omitted include_empty_rows stays omitted at schema/transform boundaries and chart-specific defaults are applied later from visualization context instead of being forced to true.
• Updated XY config-builder output so the visualization state's preferredSeriesType matches the first series layer subtype, keeping builder output aligned with shared XY default resolution.
• Fixed the date histogram interval editor to resync its local interval input when the column interval changes externally, avoiding the repeated update loop seen in multi-layer charts.

Behavior

• New charts get the chart-specific default for includeEmptyRows.
• Existing saved charts keep their current includeEmptyRows value when it is already explicit.
• API configs that omit include_empty_rows now inherit the target chart's default instead of always becoming true.
• Switching a chart or subtype to a Bar-family visualization explicitly reapplies the Bar default, even if the previous chart state had a different value.
• Layer-scoped subtype switches only rewrite the affected layer's datasource state instead of touching sibling layers in mixed charts.

How to test

1. Have Kibana ready and create a dashboard and a new Lens visualization.
2. Confirm the following charts and expected state
   • Bar, Heatmap, Pie, Treemap, Metric, Tag cloud, Waffle, Mosaic: Include empty rows off
   • Datatable: Include empty rows on

Edgy cases

• In a multi-layer XY chart, switch only one layer's subtype and confirm the sibling layer keeps its own includeEmptyRows state.
• Build or import Lens API configs that omit include_empty_rows and confirm the resulting Lens state picks up the target chart default rather than forcing true.

Notes

• line and area handling remains follow-up work for #256104