[XABT] Create separate assembly preparation tasks. (#9637)

Break down the `CollectAssemblyFilesForArchive` task further into individual tasks.

These tasks each handle a separate concern about preparing the assemblies for the apk:

- `CompressAssemblies` - Compresses assemblies using LZ4 compression (independent of ZIP compression).
- `CreateAssemblyStore` - Bundles assemblies into a single `.blob` file.
- `WrapAssembliesAsSharedLibraries` - Wraps the assemblies as shared libraries so they can go in the `lib` directory of the APK.

This should allow them to be moved to separate incremental targets in the future. For example, we do not need to compress all assemblies on every build if they haven't changed since the previous build.

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

@@ -0,0 +1,108 @@
+#nullable enable
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using Microsoft.Android.Build.Tasks;
+using Microsoft.Build.Framework;
+using Xamarin.Android.Tools;
+
+namespace Xamarin.Android.Tasks;
+
+/// <summary>
+/// Compresses assemblies using LZ4 compression before placing them in the APK.
+/// Note this is independent of whether they are stored compressed with ZIP in the APK.
+/// Our runtime bits will LZ4 decompress them at assembly load time.
+/// </summary>
+public class CompressAssemblies : AndroidTask
+{
+	public override string TaskPrefix => "CAS";
+
+	[Required]
+	public string ApkOutputPath { get; set; } = "";
+
+	public bool EmbedAssemblies { get; set; }
+
+	[Required]
+	public bool EnableCompression { get; set; }
+
+	public bool IncludeDebugSymbols { get; set; }
+
+	[Required]
+	public string ProjectFullPath { get; set; } = "";
+
+	[Required]
+	public ITaskItem [] ResolvedFrameworkAssemblies { get; set; } = [];
+
+	[Required]
+	public ITaskItem [] ResolvedUserAssemblies { get; set; } = [];
+
+	[Required]
+	public string [] SupportedAbis { get; set; } = [];
+
+	[Output]
+	public ITaskItem [] ResolvedFrameworkAssembliesOutput { get; set; } = [];
+
+	[Output]
+	public ITaskItem [] ResolvedUserAssembliesOutput { get; set; } = [];
+
+	public override bool RunTask ()
+	{
+		if (IncludeDebugSymbols || !EnableCompression || !EmbedAssemblies) {
+			ResolvedFrameworkAssembliesOutput = ResolvedFrameworkAssemblies;
+			ResolvedUserAssembliesOutput = ResolvedUserAssemblies;
+			return true;
+		}
+
+		var compressed_assemblies_info = GetCompressedAssemblyInfo ();
+
+		// Get all the user and framework assemblies we may need to compresss
+		var assemblies = ResolvedFrameworkAssemblies.Concat (ResolvedUserAssemblies).Where (asm => !(ShouldSkipAssembly (asm))).ToArray ();
+		var per_arch_assemblies = MonoAndroidHelper.GetPerArchAssemblies (assemblies, SupportedAbis, true);
+		var compressed_output_dir = Path.GetFullPath (Path.Combine (Path.GetDirectoryName (ApkOutputPath), "..", "lz4"));
+
+		foreach (var kvp in per_arch_assemblies) {
+			Log.LogDebugMessage ($"Compressing assemblies for architecture '{kvp.Key}'");
+
+			foreach (var asm in kvp.Value.Values) {
+				MonoAndroidHelper.LogIfReferenceAssembly (asm, Log);
+
+				var compressed_assembly = AssemblyCompression.Compress (Log, asm, compressed_assemblies_info, compressed_output_dir);
+
+				if (compressed_assembly.HasValue ()) {
+					Log.LogDebugMessage ($"Compressed '{asm.ItemSpec}' to '{compressed_assembly}'.");
+					asm.SetMetadata ("CompressedAssembly", compressed_assembly);
+				}
+			}
+		}
+
+		ResolvedFrameworkAssembliesOutput = ResolvedFrameworkAssemblies;
+		ResolvedUserAssembliesOutput = ResolvedUserAssemblies;
+
+		return !Log.HasLoggedErrors;
+	}
+
+	IDictionary<AndroidTargetArch, Dictionary<string, CompressedAssemblyInfo>> GetCompressedAssemblyInfo ()
+	{
+		var key = CompressedAssemblyInfo.GetKey (ProjectFullPath);
+		Log.LogDebugMessage ($"Retrieving assembly compression info with key '{key}'");
+
+		var compressedAssembliesInfo = BuildEngine4.UnregisterTaskObjectAssemblyLocal<IDictionary<AndroidTargetArch, Dictionary<string, CompressedAssemblyInfo>>> (key, RegisteredTaskObjectLifetime.Build);
+
+		if (compressedAssembliesInfo is null)
+			throw new InvalidOperationException ($"Assembly compression info not found for key '{key}'. Compression will not be performed.");
+
+		return compressedAssembliesInfo;
+	}
+
+	bool ShouldSkipAssembly (ITaskItem asm)
+	{
+		var should_skip = asm.GetMetadataOrDefault ("AndroidSkipAddToPackage", false);
+
+		if (should_skip)
+			Log.LogDebugMessage ($"Skipping {asm.ItemSpec} due to 'AndroidSkipAddToPackage' == 'true' ");
+
+		return should_skip;
+	}
+}