Revert "Fix ApplyToDerivedTypes not working for implicit styles (#9648)"

[Copilot]

• Revert MergedStyle.cs to original state (restore simple OnImplicitStyleChanged() method)
• Delete test file Maui9648.xaml
• Delete test file Maui9648.xaml.cs
• Delete benchmark file ImplicitStylesBenchmark.cs
• Add passing tests from PR Fix implicit styles with BasedOn chains breaking in 10.0.20 #33218 for issue 10.0.20 breaks implicit styles #33203
• Remove failing AppTheme tests

Description of Change

Reverts the changes from #32711 which modified how implicit styles with ApplyToDerivedTypes=true are applied.

The original behavior returns early with the first applicable implicit style instead of merging multiple styles from the type hierarchy.

Issues Fixed

Fixes #33203

Test Results

Maui33203 Tests (6/6 PASS):

• ImplicitStyleWithBasedOnKeyedStyleWorks - All 3 inflators PASSED ✅
• DerivedImplicitStyleOverridesBaseStyle - All 3 inflators PASSED ✅

Original prompt

Revert this PR #32711

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[PureWeen]

@copilot please add a note that this "Fixes #33203"

Use our standard template for the structure

[Copilot]

@copilot please add a note that this "Fixes #33203"

Use our standard template for the structure

Updated the PR description to include "Fixes #33203" and restructured it using the standard template with "Description of Change" and "Issues Fixed" sections.

[Copilot]

Pull request overview

This PR reverts the changes from PR #32711, which implemented style merging for implicit styles with ApplyToDerivedTypes=true across inheritance hierarchies. The revert restores the original behavior where only the most specific applicable implicit style is applied (early return on first match), rather than merging multiple styles from the type hierarchy.

Key Changes

• MergedStyle.cs: Restored original OnImplicitStyleChanged() logic with early return behavior instead of complex style merging
• Test deletion: Removed Maui9648.xaml and Maui9648.xaml.cs test files specific to the reverted feature
• Benchmark deletion: Removed ImplicitStylesBenchmark.cs performance benchmarks

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/Controls/src/Core/MergedStyle.cs	Reverted OnImplicitStyleChanged() to original implementation: returns on first applicable implicit style instead of collecting and merging multiple styles
src/Controls/tests/Xaml.UnitTests/Issues/Maui9648.xaml	Deleted test XAML demonstrating multi-level implicit style merging
src/Controls/tests/Xaml.UnitTests/Issues/Maui9648.xaml.cs	Deleted test code validating ApplyToDerivedTypes behavior with merged styles
src/Controls/tests/Xaml.Benchmarks/ImplicitStylesBenchmark.cs	Deleted performance benchmarks for implicit style merging scenarios

[PureWeen]

@copilot can you grab the tests from #33218 ?

and then report back if they pass

[Copilot]

@copilot can you grab the tests from #33218 ?

and then report back if they pass

Added tests from PR #33218 in commit 09cb402.

Test Results:

Test	Result
ImplicitStyleWithBasedOnKeyedStyleWorks	✅ PASS (all 3 inflators)
DerivedImplicitStyleOverridesBaseStyle	✅ PASS (all 3 inflators)
DerivedStyleOverridesBaseAppThemeBinding	❌ FAIL (all 3 inflators)
DerivedStyleOverridesBaseAppThemeBindingInDarkMode	❌ FAIL (all 3 inflators)

Summary: 6/12 tests pass. The basic Maui33203 tests pass with the revert, confirming that BasedOn keyed styles work correctly. The Maui33203AppTheme tests fail because they require the additional AppThemeBinding.cs fix from PR #33218.

[PureWeen]

@copilot alright keep the tests that are passing and remove the ones that are failing

[Copilot]

@copilot alright keep the tests that are passing and remove the ones that are failing

Done in commit 377d381. Removed the failing Maui33203AppTheme tests and kept the passing Maui33203 tests. All 6 remaining tests pass.

[rmarinho]

/azp run maui-pr-devicetests

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[PureWeen]

/backport to release/10.0.1xx-sr2

[github-actions]

Started backporting to release/10.0.1xx-sr2 (link to workflow run)

[PureWeen]

/azp run maui-pr-uitests

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).