Deprecate autolink functionality to copy useWinUI3 flags from react-native.config.js into ExperimentalFeatures.props

[Copilot]

Summary

This PR removes the deprecated functionality in ensureXAMLDialect() that allowed useWinUI3 values from react-native.config.js to override values in ExperimentalFeatures.props. This feature was confusing, unnecessary, and causing test failures.

Background

The ensureXAMLDialect() function previously had logic that:

1. Read useWinUI3 from react-native.config.js
2. If present, overwrote the corresponding value in ExperimentalFeatures.props
3. Used the config value instead of the project file value for package configuration

This behavior was problematic because:

• WinUI3 is no longer supported in Old architecture projects
• WinUI3 is not optional in New Architecture projects
• The feature was broken and causing autolink test failures
• It created confusing behavior where config could silently override project files

Changes Made

Core Logic Changes

• Simplified ensureXAMLDialect() function in autolinkWindows.ts:
  • Removed useWinUI3FromConfig variable and related logic
  • Removed the entire block (lines 740-755) that overwrote ExperimentalFeatures.props
  • Function now only uses values directly from ExperimentalFeatures.props

Test Updates

• Removed failing tests in autolink.test.ts:

  • ensureXAMLDialect - useWinUI3=true in react-native.config.js, useWinUI3=false in ExperimentalFeatures.props
  • ensureXAMLDialect - useWinUI3=false in react-native.config.js, useWinUI3=true in ExperimentalFeatures.props

• Removed broken test in projectConfig.test.ts:

  • The skipped test that was marked as broken due to this issue

Preserved Functionality

• The useWinUI3 setting in react-native.config.js remains available for other uses (e.g., project generation)
• Two tests remain that verify the function works correctly when using ExperimentalFeatures.props values directly
• All other autolink functionality is unchanged

Impact

• ✅ Resolves test failures mentioned in the issue
• ✅ Eliminates confusing behavior where config could override project files
• ✅ Minimal code changes (net reduction of 138 lines)
• ✅ No breaking changes to public APIs
• ✅ Maintains backward compatibility for other useWinUI3 usage

Testing

The remaining tests verify that:

• When useWinUI3 is not specified in config, the function uses ExperimentalFeatures.props values directly
• The function correctly handles both UseWinUI3=true and UseWinUI3=false in project files
• Package configuration is updated appropriately based on the project file values

Fixes #14601.

[anupriya13]

@copilot run yarn change and then commit.
After commit comment here "/azp run" to start the pipelines

[Copilot]

@copilot run yarn change and then commit.
After commit comment here "/azp run" to start the pipelines

I've run yarn change and committed the change file. The commit 5af8740 adds the required beachball change tracking file for the @react-native-windows/cli package.

[anupriya13]

/azp run

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