Bump external/xamarin-android-tools and fix NRT warnings

[jonathanpeppers]

Bumps external/xamarin-android-tools from 2fd1240 to ed6aab1, which enables nullable reference types in BaseTasks.

Fixes all resulting CS8600/CS8602/CS8604 NRT warnings across 18 files without using ! (null-forgiving operator).

Key changes in xamarin-android-tools

• ed6aab1 [BaseTasks] Enable nullable reference types ([AndroidClientHandler] Prevent orphaned thread in DoProcessRequest #344)
• 4fd9ae0 [Tools.AndroidSdk] Remove unused key_name variables (use ant version 1.9.8 as 1.9.7 is no longer available at ibiblio #345)
• 3bfeba6 [copilot] Add /review GitHub agentic workflow (Add support for Round Icon #346)

NRT fix patterns used

• Null-coalescing for params args: value ?? "" for nullable strings passed to params object[]
• Null checks + throw: for GetRegisteredTaskObjectAssemblyLocal/UnregisterTaskObjectAssemblyLocal results that must exist
• Null-conditional calls: Log?.LogDebugMessage(...) for nullable TaskLoggingHelper
• Remove unnecessary ?.: e.g. min_sdk?.Value -> min_sdk.Value inside if (min_sdk != null) blocks
• Nullable variable declarations: e.g. string? mono = ... for nullable return types

Supersedes #11243

[Copilot]

Pull request overview

This PR updates the external/xamarin-android-tools dependency to a commit that enables nullable reference types (NRT) in BaseTasks, and then adjusts the dotnet/android codebase to address the resulting NRT warnings in build tasks/utilities.

Changes:

• Bump external/xamarin-android-tools (enables NRT in BaseTasks) and update consumers accordingly.
• Add null-handling patterns (null checks/throws, null-coalescing for logging args, null-conditional debug logging) across MSBuild tasks and utilities.
• Tighten some internal build-pipeline assumptions by failing fast when required registered task objects are missing.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/Xamarin.Android.Build.Tasks/Utilities/RtxtParser.cs	Make debug logging tolerant of nullable logger under NRT.
src/Xamarin.Android.Build.Tasks/Utilities/FileResourceParser.cs	Adjust debug logging calls for nullable Log under NRT.
src/Xamarin.Android.Build.Tasks/Tasks/RewriteMarshalMethods.cs	Add null check for required registered NativeCodeGenState.
src/Xamarin.Android.Build.Tasks/Tasks/ResolveAndroidTooling.cs	Coalesce nullable strings when used as message args for coded errors.
src/Xamarin.Android.Build.Tasks/Tasks/Legacy/ValidateJavaVersion.cs	Coalesce nullable BuildTools version when used as message arg.
src/Xamarin.Android.Build.Tasks/Tasks/Legacy/ResolveAndroidTooling.cs	Coalesce nullable version strings when used as warning args.
src/Xamarin.Android.Build.Tasks/Tasks/GetJavaPlatformJar.cs	NRT-driven adjustments around manifest logging / message args.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateTypeMappings.cs	Add null check for required registered NativeCodeGenState.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateMainAndroidManifest.cs	Add null checks for required registered objects; avoid null output path on cleanup.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutBindings.cs	Make registered widget collection nullable and guard its use.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateAdditionalProviderSources.cs	Add null check for required registered NativeCodeGenStateCollection.
src/Xamarin.Android.Build.Tasks/Tasks/ConvertCustomView.cs	Coalesce nullable resource directory metadata when logging coded diagnostics.
src/Xamarin.Android.Build.Tasks/Tasks/CalculateLayoutCodeBehind.cs	Remove unnecessary null-conditional on non-null widgets.
src/Xamarin.Android.Build.Tasks/Tasks/BuildAppBundle.cs	Change debug log formatting while addressing NRT warnings (but see review comment).
src/Xamarin.Android.Build.Tasks/Tasks/AndroidWarning.cs	Coalesce nullable resource string / format args under NRT.
src/Xamarin.Android.Build.Tasks/Tasks/AndroidError.cs	Coalesce nullable resource string / format args under NRT.
src/Xamarin.Android.Build.Tasks/Tasks/AndroidDotnetToolTask.cs	Treat cached mono path as nullable under NRT.
src/Xamarin.Android.Build.Tasks/Tasks/Aapt2Compile.cs	Ensure non-null enumerable passed to async processing under NRT.

Comments suppressed due to low confidence (2)

src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutBindings.cs:213

• After the widgets is null || widgets.Count == 0 guard, widgets is known to be non-null, but later the code still uses the null-forgiving operator (widgets!) when calling GenerateSource. Since this PR aims to fix NRT warnings without !, please refactor to avoid the null-forgiving operator here (e.g., by passing the non-null widgets variable directly after the guard).

			string collectionKey;
			if (!GetRequiredMetadata (item, CalculateLayoutCodeBehind.WidgetCollectionKeyMetadata, out collectionKey))
				return;

			ICollection<LayoutWidget>? widgets = BuildEngine4.GetRegisteredTaskObjectAssemblyLocal<ICollection<LayoutWidget>> (ProjectSpecificTaskObjectKey (collectionKey), RegisteredTaskObjectLifetime.Build);
			if (widgets is null || widgets.Count == 0) {
				string inputPaths = String.Join ("; ", resourceItems.Select (i => i.ItemSpec));
				LogCodedWarning ("XA4222", Properties.Resources.XA4222, inputPaths);
				return;
			}

src/Xamarin.Android.Build.Tasks/Utilities/FileResourceParser.cs:76

• ResourceParser.Log is nullable, but this method now mixes Log?.LogDebugMessage(...) with later unconditional Log.LogDebugMessage(...) calls in the same method body. If Log is required for this parser, consider validating Log is non-null once at the start of Parse() (and then using Log. consistently) instead of sprinkling null-conditional calls (which can also leave CS8602 warnings on the remaining Log. usages).

		public IList<R> Parse (string resourceDirectory, IEnumerable<string> additionalResourceDirectories, IEnumerable<string> aarLibraries, Dictionary<string, string> resourceMap)
		{
			Log?.LogDebugMessage ($"Parsing Directory {resourceDirectory}");
			publicXml = LoadPublicXml ();
			var result = new List<R> ();
			Dictionary<string, ICollection<R>> resources = new Dictionary<string, ICollection<R>> ();
			foreach (var knownType in RtxtParser.knownTypes) {
				if (knownType == "styleable") {
					resources.Add (knownType, new List<R> ());
					continue;
				}
				resources.Add (knownType, new SortedSet<R> (new RComparer ()));
			}
			foreach (var dir in Directory.EnumerateDirectories (resourceDirectory, "*", SearchOption.TopDirectoryOnly)) {
				foreach (var file in Directory.EnumerateFiles (dir, "*.*", SearchOption.AllDirectories)) {
					ProcessResourceFile (file, resources);
				}
			}
			foreach (var dir in additionalResourceDirectories ?? []) {
				Log.LogDebugMessage ($"Processing Directory {dir}");
				if (Directory.Exists (dir)) {
					foreach (var file in Directory.EnumerateFiles (dir, "*.*", SearchOption.AllDirectories)) {
						ProcessResourceFile (file, resources);
					}
				} else {
					Log.LogDebugMessage ($"Skipping non-existent directory: {dir}");
				}