[Xamarin.Android.Build.Tasks] lazily populate Resource lookup

Fixes: dotnet#7684

Comparing .NET 7 to main, I noticed:

    .NET 7
    Task LinkAssembliesNoShrink 4ms
    main/.NET 8
    Task LinkAssembliesNoShrink 101ms

Under `dotnet trace` a lot of the time was spent in:

    94.74ms MonoDroid.Tuner.FixLegacyResourceDesignerStep.LoadDesigner()

Reviewing the code, I think we can "lazily" call the `LoadDesigner()`
method. It creates a `Dictionary` that isn't used until the
`FixBody()` method.

I also updated one log message to only log duplicates, as it was
logging hundreds of lines:

    if (output.ContainsKey (key)) {
        LogMessage ($"          Found duplicate {key}");
    } else {
        output.Add (key, property.GetMethod);
    }

Which also showed up in `dotnet trace`:

    25.58ms Microsoft.Android.Build.Tasks.MSBuildExtensions.LogDebugMessage()

With these changes, I instead get:

    Task LinkAssembliesNoShrink 5ms

Which is probably ~the same performance as before or plenty good enough!

src/Xamarin.Android.Build.Tasks/Linker/MonoDroid.Tuner/FixLegacyResourceDesignerStep.cs

@@ -68,7 +68,6 @@ protected override void LoadDesigner ()
 				return;
 			}
 			lookup = BuildResourceDesignerPropertyLookup (designerType);
-			return;
 		}
 
 		internal override bool ProcessAssemblyDesigner (AssemblyDefinition assembly)
@@ -114,9 +113,10 @@ Dictionary<string, MethodDefinition> BuildResourceDesignerPropertyLookup (TypeDe
 				foreach (PropertyDefinition property in definition.Properties)
 				{
 					string key = $"{definition.Name}::{property.Name}";
-					if (!output.ContainsKey (key)) {
-						LogMessage ($"          Adding {key}");
-						output.Add(key, property.GetMethod);
+					if (output.ContainsKey (key)) {
+						LogMessage ($"          Found duplicate {key}");
+					} else {
+						output.Add (key, property.GetMethod);
 					}
 				}
 			}
@@ -125,6 +125,10 @@ Dictionary<string, MethodDefinition> BuildResourceDesignerPropertyLookup (TypeDe
 
 		protected override void FixBody (MethodBody body, TypeDefinition designer)
 		{
+			// This is expected to be null for the first call, in <LinkAssembliesNoShrink/>
+			if (lookup == null)
+				LoadDesigner ();
+
 			// replace
 			// IL_0068: ldsfld int32 Xamarin.Forms.Platform.Android.Resource/Layout::Toolbar
 			// with

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

@@ -67,8 +67,6 @@ public override bool RunTask ()
 				var fixAbstractMethodsStep = new FixAbstractMethodsStep (resolver, cache, Log);
 				var addKeepAliveStep = new AddKeepAlivesStep (resolver, cache, Log, UsingAndroidNETSdk);
 				var fixLegacyResourceDesignerStep = new FixLegacyResourceDesignerStep (resolver, cache, Log);
-				if (UseDesignerAssembly)
-					fixLegacyResourceDesignerStep.Load ();
 				for (int i = 0; i < SourceFiles.Length; i++) {
 					var source = SourceFiles [i];
 					var destination = DestinationFiles [i];
@@ -140,10 +138,6 @@ public FixLegacyResourceDesignerStep (DirectoryAssemblyResolver resolver, TypeDe
 				this.logger = logger;
 			}
 
-			public void Load () {
-				LoadDesigner ();
-			}
-
 			public override void LogMessage (string message)
 			{
 				logger.LogDebugMessage ("{0}", message);