[xabt] Fix XA4211 warning message to use $(TargetPlatformVersion) (#10197)

Fixes: #10196

Customers reported that the XA4211 warning message contains outdated
property references and blank values for .NET 6+ projects:

    AndroidManifest.xml: Warning XA4211 : AndroidManifest.xml //uses-sdk/@android:targetSdkVersion '34' is less than $(TargetFrameworkVersion) ''. Using API-35 for ACW compilation.

The warning was written during the Xamarin.Android timeframe and needs
updating for .NET 6+:

- **Property name**: `$(TargetFrameworkVersion)` should be
  `$(TargetPlatformVersion)` for .NET 6+
- **Blank values**: The empty `''` appears because the message
  references the wrong property

## Changes

Updated the XA4211 message in `Resources.resx`:
- Changed message text from `$(TargetFrameworkVersion)` to
  `$(TargetPlatformVersion)`
- Updated comment documentation to reference the correct property
- Updated parameter description to reflect "target platform version
  number"

This occurs when developers explicitly set a lower target SDK version
in their AndroidManifest.xml:

    <uses-sdk android:targetSdkVersion="34" />

The warning is reasonable to show, but the message text should be
accurate for modern .NET Android projects.

Author: Copilot

src/Xamarin.Android.Build.Tasks/Properties/Resources.resx

@@ -604,10 +604,10 @@ Either change the value in the AndroidManifest.xml to match the $(SupportedOSPla
     <comment>The following are literal names and should not be translated: Mono.Android.Export.dll, ExportAttribute, ExportFieldAttribute.</comment>
   </data>
   <data name="XA4211" xml:space="preserve">
-    <value>AndroidManifest.xml //uses-sdk/@android:targetSdkVersion '{0}' is less than $(TargetFrameworkVersion) '{1}'. Using API-{2} for ACW compilation.</value>
-    <comment>The following are literal names and should not be translated: AndroidManifest.xml, //uses-sdk/@android:targetSdkVersion , $(TargetFrameworkVersion), API-{2}, ACW
+    <value>AndroidManifest.xml //uses-sdk/@android:targetSdkVersion '{0}' is less than $(TargetPlatformVersion) '{1}'. Using API-{2} for ACW compilation.</value>
+    <comment>The following are literal names and should not be translated: AndroidManifest.xml, //uses-sdk/@android:targetSdkVersion , $(TargetPlatformVersion), API-{2}, ACW
 {0} - The target SDK version number
-{1} - The target framework version number
+{1} - The $(TargetPlatformVersion) number
 {2} - The API version number</comment>
   </data>
   <data name="XA4213" xml:space="preserve">

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

@@ -35,6 +35,8 @@ public class GetJavaPlatformJar : AndroidTask
 
 		public string AndroidSdkDirectory { get; set; }
 
+		public string TargetPlatformVersion { get; set; }
+
 		[Output]
 		public string JavaPlatformJarPath { get; set; }
 
@@ -118,6 +120,9 @@ string GetTargetSdkVersion (string target, XAttribute target_sdk)
 			string targetFrameworkVersion = MonoAndroidHelper.SupportedVersions.GetIdFromApiLevel (AndroidSdkPlatform);
 			string targetSdkVersion       = MonoAndroidHelper.SupportedVersions.GetIdFromApiLevel (target);
 
+			// For .NET 6+ projects, use TargetPlatformVersion directly
+			string targetPlatformVersionDisplay = !string.IsNullOrEmpty (TargetPlatformVersion) ? TargetPlatformVersion : "";
+
 			if (!int.TryParse (targetFrameworkVersion, out int frameworkSdk)) {
 				// AndroidSdkPlatform is likely a *preview* API level; use it.
 				Log.LogWarningForXmlNode (
@@ -127,7 +132,7 @@ string GetTargetSdkVersion (string target, XAttribute target_sdk)
 						message:          Properties.Resources.XA4211,
 						messageArgs:      new [] {
 							targetSdkVersion,
-							MonoAndroidHelper.SupportedVersions.GetIdFromFrameworkVersion (targetFrameworkVersion),
+							targetPlatformVersionDisplay,
 							MonoAndroidHelper.SupportedVersions.GetIdFromApiLevel (targetFrameworkVersion),
 						}
 				);
@@ -142,7 +147,7 @@ string GetTargetSdkVersion (string target, XAttribute target_sdk)
 						message:          Properties.Resources.XA4211,
 						messageArgs:      new [] {
 							targetSdkVersion,
-							MonoAndroidHelper.SupportedVersions.GetIdFromFrameworkVersion (targetFrameworkVersion),
+							targetPlatformVersionDisplay,
 							MonoAndroidHelper.SupportedVersions.GetIdFromApiLevel (targetFrameworkVersion),
 						}
 				);

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Tooling.targets

@@ -97,6 +97,7 @@ projects.
         BuildingInsideVisualStudio="$(BuildingInsideVisualStudio)"
         SupportedOSPlatformVersion="$(SupportedOSPlatformVersion)"
         TargetFramework="$(TargetFramework)"
+        TargetPlatformVersion="$(TargetPlatformVersion)"
     >
       <Output TaskParameter="JavaPlatformJarPath" PropertyName="JavaPlatformJarPath" />
       <Output TaskParameter="TargetSdkVersion"    PropertyName="_AndroidTargetSdkVersion" />