[Tests] Bump default AGP to 9.1.0 for compileSdk 36 compatibility

[simonrozsival]

Summary

Bumps the default Android Gradle Plugin (AGP) version in the test infrastructure from 8.5.0 to 9.1.0 to fix Gradle test failures caused by an AGP/compileSdk version mismatch.

Problem

The default AgpVersion was hardcoded to 8.5.0 in AndroidGradleProject.cs, while CompileSdk is dynamically derived from AndroidLatestStableApiLevel (now 36). AGP 8.5.0 only supports up to compileSdk 34, causing a Gradle configuration-cache serialization crash in MergeJavaResourceTask for tests like BuildMultipleModules(MonoVM).

See the AGP compatibility table for details.

Changes

• AndroidGradleProject.cs: Bump default AgpVersion from "8.5.0" → "9.1.0" and set default GradleVersion to "9.1.0"
• AndroidGradleProject.cs: Add optional compileSdk parameter to CreateDefault overload
• AndroidGradleProjectTests.cs: Fix BindLibraryWithMultipleGradleVersions — the AGP 8.5.0 test case now uses compileSdk = 34 (within its supported range), while the AGP 9.0.0 case uses the current default

Customer Impact

None — these changes are test-infrastructure only (Xamarin.ProjectTools namespace). Real customer projects specify their own AGP version in their build.gradle.kts.

Fixes #11042

[Copilot]

Pull request overview

Updates the Gradle test infrastructure defaults to use newer Android Gradle Plugin (AGP) and Gradle versions, addressing test failures when compileSdk is at/near the current stable API level.

Changes:

• Bump default AGP version in AndroidGradleProject from 8.5.0 to 9.1.0 and set a default Gradle wrapper version (9.1.0).
• Extend AndroidGradleProject.CreateDefault (versioned overload) with an optional compileSdk parameter.
• Adjust BindLibraryWithMultipleGradleVersions test data to use compileSdk = 34 for AGP 8.5.0, and current default for newer AGP.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/AndroidGradleProject.cs	Updates default AGP/Gradle versions and adds compileSdk override support when creating default Gradle projects.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AndroidGradleProjectTests.cs	Updates parameterized test data and signature to include compileSdk for version-compat test coverage.

[Copilot]

The XML doc for GradleVersion says the wrapper version is used “if null or empty”, but the property is now initialized to "9.1.0" by default. Consider updating this comment to reflect the new default behavior (i.e., wrapper version will be overridden unless callers explicitly set it to null/empty).

Suggested change

	/// If null or empty, the Gradle wrapper version generated by gradle init is used.
	/// Defaults to "9.1.0". If set to null or empty, the Gradle wrapper version generated by gradle init is used.

[Copilot]

CreateDefault’s summary mentions only AGP/Gradle versions, but the method now also takes an optional compileSdk parameter. Please update the XML docs to mention what compileSdk controls and what default is used when it’s omitted.

Suggested change

	/// Creates a default Gradle project with specified AGP and Gradle versions.
	/// </summary>
	/// Creates a default Gradle project with specified AGP, Gradle, and compileSdk versions.
	/// When <paramref name="compileSdk" /> is <c>null</c>, the default value
	/// <see cref="XABuildConfig.AndroidDefaultTargetDotnetApiLevel.Major" /> is used.
	/// </summary>
	/// <param name="compileSdk">
	/// The Android compileSdk level to use for the created module. If omitted or <c>null</c>,
	/// the project will use <see cref="XABuildConfig.AndroidDefaultTargetDotnetApiLevel.Major" />.
	/// </param>

[Copilot]

PR description states the default compileSdk is derived from AndroidLatestStableApiLevel, but here the default/fallback is XABuildConfig.AndroidDefaultTargetDotnetApiLevel.Major. Please align the PR description with the implementation (or switch to AndroidLatestStableApiLevel if that’s the intended source).