Fail on conflicting TestingPlatformBuilderHook IDs

[Copilot]

TestingPlatformSelfRegisteredExtensions previously collapsed duplicate TestingPlatformBuilderHook items by ID and kept the first entry. If two packages reused an ID with different metadata, one extension disappeared silently.

• Duplicate validation

  • Detects duplicate hook IDs with conflicting DisplayName or TypeFullName.
  • Logs an MSBuild error instead of generating a partially registered test app.

• Exact duplicate handling

  • Keeps deduplication for truly identical hook entries.
  • Generates registration code from the validated, deduplicated hook set.

• Regression coverage

  • Adds unit coverage for exact duplicate deduplication.
  • Adds unit coverage for conflicting duplicate IDs failing generation.

<TestingPlatformBuilderHook Include="hook">
  <DisplayName>First</DisplayName>
  <TypeFullName>Contoso.FirstHook</TypeFullName>
</TestingPlatformBuilderHook>

<TestingPlatformBuilderHook Include="hook">
  <DisplayName>Second</DisplayName>
  <TypeFullName>Contoso.SecondHook</TypeFullName>
</TestingPlatformBuilderHook>

The above now fails the build instead of silently registering only the first hook.

[Evangelink]

/review

[Copilot]

Pull request overview

This PR strengthens TestingPlatformSelfRegisteredExtensions (MSBuild task) by validating TestingPlatformBuilderHook items for duplicate IDs: exact duplicates are deduplicated, while conflicting duplicates now fail the build to avoid silently dropping an extension.

Changes:

• Added validation + deduplication for SelfRegisteredExtensionsBuilderHook items, failing on conflicting metadata for the same Include/ID.
• Updated code generation to use the validated, deduplicated hook set.
• Added unit tests covering exact-duplicate deduplication and conflicting-duplicate failure behavior.

Show a summary per file

File	Description
test/UnitTests/Microsoft.Testing.Platform.MSBuild.UnitTests/MSBuildTests.cs	Adds unit coverage for deduplication and for build failure when duplicate hook IDs have conflicting metadata.
src/Platform/Microsoft.Testing.Platform.MSBuild/Tasks/TestingPlatformAutoRegisteredExtensions.cs	Implements hook validation/deduplication and wires code generation to the validated hook list.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1