…27848)

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## **Description**
Support webcredential for ios google login
Part 2/4 - Add feature flag 

This pr add feature flag for the ios google login


PR list
Part 1/ 4 - #27741
Part 2/ 4 - #27848
Part 3/ 4 - #27850
Part 4/ 4 - TBA

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## **Changelog**

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CHANGELOG entry: added legacyIosGoogleConfigEnabled feature flag

## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]
```

## **Screenshots/Recordings**

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before and after of your change. -->

### **Before**

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### **After**

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## **Pre-merge author checklist**

- [ ] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
- [ ] I've included tests if applicable
- [ ] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.



<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: adds a new remote feature flag and selector with env
override, without changing authentication flow yet; main risk is
misconfiguration since the selector defaults to enabled.
> 
> **Overview**
> Adds a new remote feature flag, `legacyIosGoogleConfigEnabled`,
including registry metadata and a dedicated selector
`selectLegacyIosGoogleConfigEnabled` (defaulting to `true`) that can be
force-overridden via `MM_LEGACY_IOS_GOOGLE_CONFIG_ENABLED`.
> 
> Includes unit tests covering default/remote/env override behavior, and
updates `babel.config.tests.js` to avoid inlining env vars for the new
selector and its tests.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
ca7e813. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->