[xabt] Fix NRT annotations in Xamarin.Android.Build.Tasks, part 1 (#10327)

Context: #10326

This PR systematically updates Nullable Reference Types (NRT)
annotations across the `src/Xamarin.Android.Build.Tasks/Tasks/`
directory to follow the repository's coding guidelines as defined in
`.github/copilot-instructions.md`.

## Changes Made

This pull request primarily focuses on code modernization and cleanup
for the `Xamarin.Android.Build.Tasks` project. The changes include
replacing `Array.Empty<T>()` with `[]` for initializing arrays and
switching from `string.Empty` to `""` for string initialization.
Additionally, nullable annotations have been enabled in a utility file
to improve code safety. These updates aim to simplify the codebase and
align it with modern C# conventions.

### Code Modernization

* Replaced `Array.Empty<T>()` with `[]` for array initialization
  across multiple files. This change simplifies array initialization
  syntax. Examples include `RuntimePackLibraryDirectories`,
  `ReferenceSatellitePaths`, and `InputAssemblies`.

* Updated string initialization from `string.Empty` to `""` for
  consistency and brevity. Examples include `CodeGenerationTarget`,
  `OutputDirectory`, and `NuGetPackageId`.

### Nullable Annotations

* Enabled nullable annotations in `DummyCustomAttributeProvider.cs` to
  improve code safety and nullability handling.

### Logical Enhancements

* Added null checks in `GenerateResourceDesignerAssembly.cs` to skip
  processing resources with null identifiers or type names, ensuring
  robustness in resource handling.

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

Author: Copilot

src/Xamarin.Android.Build.Tasks/Tasks/Aapt2.cs

@@ -130,7 +130,7 @@ protected bool LogAapt2EventsFromOutput (string singleLine, MessageImportance me
 				return true;
 
 			var match = AndroidRunToolTask.AndroidErrorRegex.Match (singleLine.Trim ());
-			string file = string.Empty;
+			string file = "";
 
 			if (match.Success) {
 				file = match.Groups ["file"].Value;

src/Xamarin.Android.Build.Tasks/Tasks/Aapt2Link.cs

@@ -311,7 +311,7 @@ string [] GenerateCommandLineCommands (string ManifestFile, string? currentAbi,
 			}
 
 			if (hasAssetsErrors) {
-				return Array.Empty<string> ();
+				return [];
 			}
 
 			if (!ProguardRuleOutput.IsNullOrEmpty ()) {

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

@@ -80,7 +80,7 @@ public override bool RunTask ()
 			ReadSymbols = ReadSymbols,
 		};
 
-		Dictionary<AndroidTargetArch, Dictionary<string, ITaskItem>> perArchAssemblies = MonoAndroidHelper.GetPerArchAssemblies (ResolvedAssemblies, Array.Empty<string> (), validate: false);
+		Dictionary<AndroidTargetArch, Dictionary<string, ITaskItem>> perArchAssemblies = MonoAndroidHelper.GetPerArchAssemblies (ResolvedAssemblies, [], validate: false);
 
 		AssemblyPipeline? pipeline = null;
 		var currentArch = AndroidTargetArch.None;

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

@@ -133,7 +133,7 @@ internal override CommandLineBuilder GetCommandLineBuilder ()
 			cmd.AppendSwitchIfNotNull ("--modules ", string.Join (",", modules));
 			cmd.AppendSwitchIfNotNull ("--output ", Output);
 			cmd.AppendSwitchIfNotNull ("--config ", temp);
-			foreach (var file in MetaDataFiles ?? Array.Empty<ITaskItem> ()) {
+			foreach (var file in MetaDataFiles ?? []) {
 				cmd.AppendSwitch ($"--metadata-file={file.ItemSpec}");
 			}
 			return cmd;

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

@@ -25,7 +25,7 @@ public override bool RunTask ()
 				jarFiles = jarFiles.Concat (JavaLibraries);
 			else if (JavaLibraries != null)
 				jarFiles = JavaLibraries;
-			var jarFilePaths = (LibraryProjectJars ?? Array.Empty<ITaskItem> ()).Concat (jarFiles ?? Array.Empty<ITaskItem> ()).Select (j => j.ItemSpec);
+			var jarFilePaths = (LibraryProjectJars ?? []).Concat (jarFiles ?? []).Select (j => j.ItemSpec);
 
 			// Remove duplicate identical jars by name, size and content, and reject any jars that conflicts by name (i.e. different content).
 			var jars = MonoAndroidHelper.DistinctFilesByContent (jarFilePaths).ToArray ();

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

@@ -54,7 +54,7 @@ public class CollectNativeFilesForArchive : AndroidTask
 	public string AndroidBinUtilsDirectory { get; set; } = "";
 
 	[Required]
-	public ITaskItem[] RuntimePackLibraryDirectories { get; set; } = Array.Empty<ITaskItem> ();
+	public ITaskItem[] RuntimePackLibraryDirectories { get; set; } = [];
 
 	[Required]
 	public string IntermediateOutputPath { get; set; } = "";

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

@@ -19,7 +19,7 @@ public class CollectRuntimeConfigFilesForArchive : AndroidTask
 	public string AndroidBinUtilsDirectory { get; set; } = "";
 
 	[Required]
-	public ITaskItem[] RuntimePackLibraryDirectories { get; set; } = Array.Empty<ITaskItem> ();
+	public ITaskItem[] RuntimePackLibraryDirectories { get; set; } = [];
 
 	[Required]
 	public string IntermediateOutputPath { get; set; } = "";

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

@@ -22,13 +22,13 @@ public class GenerateJavaCallableWrappers : AndroidTask
 	public override string TaskPrefix => "JCW";
 
 	[Required]
-	public string CodeGenerationTarget { get; set; } = string.Empty;
+	public string CodeGenerationTarget { get; set; } = "";
 
 	[Required]
-	public string OutputDirectory { get; set; } = string.Empty;
+	public string OutputDirectory { get; set; } = "";
 
 	[Required]
-	public string PackageNamingPolicy { get; set; } = string.Empty;
+	public string PackageNamingPolicy { get; set; } = "";
 
 	[Required]
 	public ITaskItem [] ResolvedAssemblies { get; set; } = [];

src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutBindings.CSharpBindingGenerator.cs

@@ -14,7 +14,7 @@ sealed class CSharpBindingGenerator : BindingGenerator
 		{
 			const string BindingPartialClassBackingFieldName = "__layout_binding";
 
-			string codebehindDir = string.Empty;
+			string codebehindDir = "";
 			protected override string LineCommentString => "//";
 			protected override string DocCommentString => "///";
 			public override string LanguageName => "C#";

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

@@ -41,7 +41,7 @@ public override bool RunTask ()
 			ResourceDirectory = Path.GetFullPath (ResourceDirectory);
 
 			// Create our capitalization maps so we can support mixed case resources
-			foreach (var item in Resources ?? Array.Empty<ITaskItem>()) {
+			foreach (var item in Resources ?? []) {
 				var path = Path.GetFullPath (item.ItemSpec);
 				if (!path.StartsWith (ResourceDirectory, StringComparison.OrdinalIgnoreCase)) {
 					Log.LogDebugMessage ($"Skipping {item}. Path is not include the '{ResourceDirectory}'");
@@ -55,7 +55,7 @@ public override bool RunTask ()
 
 				AddRename (name.Replace ('/', Path.DirectorySeparatorChar), logical_name.Replace ('/', Path.DirectorySeparatorChar));
 			}
-			foreach (var additionalDir in AdditionalResourceDirectories ?? Array.Empty<ITaskItem>()) {
+			foreach (var additionalDir in AdditionalResourceDirectories ?? []) {
 				var dir = Path.Combine (ProjectDir, Path.GetDirectoryName (additionalDir.ItemSpec));
 				var file = Path.Combine (dir, "__res_name_case_map.txt");
 				if (!File.Exists (file)) {
@@ -72,7 +72,7 @@ public override bool RunTask ()
 				}
 			}
 			var resmap = ".net/__res_name_case_map.txt";
-			foreach (var aar in AarLibraries ??  Array.Empty<string>()) {
+			foreach (var aar in AarLibraries ??  []) {
 				Log.LogDebugMessage ($"Processing Aar file {aar}");
 				if (!File.Exists (aar)) {
 					Log.LogDebugMessage ($"Skipping non-existent aar: {aar}");