[xabt] Fix NRT annotations in Xamarin.Android.Build.Tasks, part 2 (#10335)

Context: #10326

This PR adds nullable reference type (NRT) annotations to C# files in
the `src\Xamarin.Android.Build.Tasks\Utilities\` directory while
maintaining compatibility with existing MSBuild scenarios and tests.

## Key Changes

**Nullable Reference Type Enablement:**

- Added `#nullable enable` directive to 51 utility files that were
  missing nullable annotations
- Converted `FileResourceParser.cs` from `#nullable disable` to
  `#nullable enable` with proper nullable annotations
- Fixed nullable reference type violations for variables, return
  types, and parameters

**Cross-Project Compatibility:**

- Used `String.IsNullOrEmpty()` instead of extension methods in shared
  utility files to avoid compilation errors across different project
  namespaces
- Ensured MonoAndroidHelper files work correctly across multiple
  consuming projects

**MSBuild Task Compatibility:**

- Made `JavaResgenInputFile` property in `GenerateResourceDesigner`
  task optional (nullable) to maintain compatibility with existing
  tests and managed resource generator usage
- Added proper null validation only when the JavaResourceParser path
  is used, preserving the dual-mode functionality
  (ManagedResourceParser vs JavaResourceParser)
- Fixed MSBuild test failures while maintaining backward compatibility

**Cleanup:**

- Reverted `JavaResourceParser.cs` completely per reviewer feedback

The changes improve type safety through proper nullable reference type
annotations while ensuring all existing functionality continues to
work correctly, including unit tests and cross-project compilation
scenarios.

Co-authored-by: Jonathan Peppers <[email protected]>

Author: Copilot

src/Xamarin.Android.Build.Tasks/Tasks/GenerateResourceDesigner.cs

@@ -86,6 +86,9 @@ public override bool RunTask ()
 				var parser = new ManagedResourceParser () { Log = Log, JavaPlatformDirectory = javaPlatformDirectory, ResourceFlagFile = ResourceFlagFile };
 				resources = parser.Parse (ResourceDirectory, RTxtFile ?? string.Empty, AdditionalResourceDirectories?.Select (x => x.ItemSpec), IsApplication, resource_fixup);
 			} else {
+				if (JavaResgenInputFile == null) {
+					throw new ArgumentNullException (nameof (JavaResgenInputFile));
+				}
 				var parser = new JavaResourceParser () { Log = Log };
 				resources = parser.Parse (JavaResgenInputFile, IsApplication, resource_fixup);
 			}

src/Xamarin.Android.Build.Tasks/Tasks/GenerateRtxt.cs

@@ -34,7 +34,7 @@ public override bool RunTask ()
 
 			var javaPlatformDirectory = JavaPlatformJarPath.IsNullOrEmpty () ? "" : Path.GetDirectoryName (JavaPlatformJarPath);
 			var parser = new FileResourceParser () { Log = Log, JavaPlatformDirectory = javaPlatformDirectory, ResourceFlagFile = ResourceFlagFile};
-			var resources = parser.Parse (ResourceDirectory, AdditionalResourceDirectories, AarLibraries, resource_fixup);
+			var resources = parser.Parse (ResourceDirectory, AdditionalResourceDirectories ?? [], AarLibraries ?? [], resource_fixup);
 
 			// only update if it changed.
 			writer.Write (RTxtFile, resources);

src/Xamarin.Android.Build.Tasks/Utilities/ACWMapGenerator.cs

@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.IO;

src/Xamarin.Android.Build.Tasks/Utilities/Aapt2Daemon.cs

@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
@@ -252,7 +253,7 @@ private void Aapt2DaemonStart ()
 						}
 						// wait for the file we expect to be created. There can be a delay between
 						// the daemon saying "Done" and the file finally being written to disk.
-						if (!string.IsNullOrEmpty (job.OutputFile) && !errored) {
+						if (!job.OutputFile.IsNullOrEmpty () && !errored) {
 							while (!File.Exists (job.OutputFile)) {
 								// If either the AsyncTask.CancellationToken or tcs.Token are cancelled, we need to abort
 								tcs.Token.ThrowIfCancellationRequested ();

src/Xamarin.Android.Build.Tasks/Utilities/AndroidResource.cs

@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
@@ -91,7 +92,7 @@ static bool ResourceNeedsToBeLowerCased (string? value, string? resourceBasePath
 			// path to the msbuild's intermediate output directory and that location can be changed by the
 			// user. It's better to be safe than sorry.
 			resourceBasePath = resourceBasePath?.Trim ();
-			if (string.IsNullOrEmpty (resourceBasePath))
+			if (resourceBasePath.IsNullOrEmpty ())
 				return true;
 
 			// Avoid resource names that are all whitespace
@@ -159,7 +160,7 @@ private static void TryFixResourceAlias (XElement elem, string? resourceBasePath
 			//   <item type="layout" name="">@layout/Page1</item>
 			//   <item type="layout" name="">@drawable/Page1</item>
 			// and corrects the alias to be lower case.
-			if (elem.Name == "item" && !string.IsNullOrEmpty(elem.Value) ) {
+			if (elem.Name == "item" && !elem.Value.IsNullOrEmpty() ) {
 				string value = elem.Value.Trim();
 				Match m = r.Match (value);
 				if (m.Success) {

src/Xamarin.Android.Build.Tasks/Utilities/AndroidRuntime.cs

@@ -1,3 +1,4 @@
+#nullable enable
 namespace Xamarin.Android.Tasks;
 
 public enum AndroidRuntime

src/Xamarin.Android.Build.Tasks/Utilities/ApplicationConfig.cs

@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 
 namespace Xamarin.Android.Tasks

src/Xamarin.Android.Build.Tasks/Utilities/ApplicationConfigCLR.cs

@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 
 namespace Xamarin.Android.Tasks;

src/Xamarin.Android.Build.Tasks/Utilities/AssemblyCompression.cs

@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.Buffers;
@@ -37,7 +38,7 @@ public AssemblyData (string sourcePath, uint descriptorIndex)
 
 			public void SetData (string sourcePath, uint descriptorIndex)
 			{
-				if (String.IsNullOrEmpty (sourcePath))
+				if (sourcePath.IsNullOrEmpty ())
 					throw new ArgumentException ("must not be null or empty", nameof (sourcePath));
 				SourcePath = sourcePath;
 				DescriptorIndex = descriptorIndex;
@@ -62,7 +63,7 @@ static CompressionResult Compress (AssemblyData data, string outputFilePath)
 
 			var outputDirectory = Path.GetDirectoryName (outputFilePath);
 
-			if (String.IsNullOrEmpty (outputDirectory))
+			if (outputDirectory.IsNullOrEmpty ())
 				throw new ArgumentException ("must not be null or empty", nameof (outputDirectory));
 
 			Directory.CreateDirectory (outputDirectory);
@@ -172,7 +173,7 @@ static string GetCompressedAssemblyOutputDirectory (ITaskItem assembly, string c
 			string subDirectory = assembly.GetMetadata ("DestinationSubDirectory");
 			string abi = MonoAndroidHelper.GetAssemblyAbi (assembly);
 
-			if (!string.IsNullOrEmpty (subDirectory) && !(subDirectory.EndsWith ($"{abi}/", StringComparison.Ordinal) || subDirectory.EndsWith ($"{abi}\\", StringComparison.Ordinal))) {
+			if (!subDirectory.IsNullOrEmpty () && !(subDirectory.EndsWith ($"{abi}/", StringComparison.Ordinal) || subDirectory.EndsWith ($"{abi}\\", StringComparison.Ordinal))) {
 				assemblyOutputDir = Path.Combine (compressedOutputDir, abi, subDirectory);
 			} else {
 				assemblyOutputDir = Path.Combine (compressedOutputDir, abi);

src/Xamarin.Android.Build.Tasks/Utilities/AssemblyIdentityMap.cs

@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
@@ -12,7 +13,7 @@ internal class AssemblyIdentityMap
 		public void Load (string mapFile)
 		{
 			map.Clear ();
-			if (string.IsNullOrWhiteSpace (mapFile) || !File.Exists (mapFile))
+			if (mapFile.IsNullOrWhiteSpace () || !File.Exists (mapFile))
 				return;
 			foreach (var s in File.ReadLines (mapFile)) {
 				if (!map.Contains (s))