[Xamarin.Android.Build.Tasks] emit XA1040 for experimental runtimes (#9834)

MonoVM is currently the default (and supported!) runtime for .NET for
Android.  Emit warning XA1040 when the user opts into using the
experimental runtimes, such as:

  * CoreCLR, via `$(UseMonoRuntime)=false`
  * NativeAOT, via `$(PublishAot)=true`

For example:

	warning XA1040: The NativeAOT runtime on Android is an experimental feature and not yet suitable for production use.
	  File issues at: https://github.com/dotnet/android/issues

If desired, you can opt out of the warning completely with
`$(EnablePreviewFeatures)=true`, or use existing MSBuild
mechanisms to suppress it.

Author: jonathanpeppers

Documentation/docs-mobile/messages/xa1040.md

@@ -0,0 +1,31 @@
+---
+title: .NET for Android warning XA1040
+description: XA1040 warning code
+ms.date: 02/24/2025
+---
+# .NET for Android warning XA1040
+
+## Example messages
+
+```
+warning XA1040: The CoreCLR runtime on Android is an experimental feature and not yet suitable for production use. File issues at: https://github.com/dotnet/android/issues
+warning XA1040: The NativeAOT runtime on Android is an experimental feature and not yet suitable for production use. File issues at: https://github.com/dotnet/android/issues
+```
+
+## Issue
+
+MonoVM is the default, supported runtime for .NET for Android.
+
+Other runtimes are currently experimental, such as:
+
+* CoreCLR, used via `$(UseMonoRuntime)=false`
+* NativeAOT, used via `$(PublishAot)=true`
+
+## Solution
+
+To silence this warning, you can either:
+
+* Use MonoVM by removing `$(UseMonoRuntime)=false` or
+  `$(PublishAot)=true` from your project file.
+
+* Set `$(EnablePreviewFeatures)` to `true` in your project file.

src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs

@@ -1016,6 +1016,11 @@ To use a custom JDK path for a command line build, set the 'JavaSdkDirectory' MS
     <value>The Android Support libraries are not supported in .NET 9 and later, please migrate to AndroidX. See https://aka.ms/net-android/androidx for more details.</value>
     <comment>The following are literal names and should not be translated: Android Support, AndroidX, .NET.</comment>
   </data>
+  <data name="XA1040" xml:space="preserve">
+    <value>The {0} runtime on Android is an experimental feature and not yet suitable for production use. File issues at: https://github.com/dotnet/android/issues</value>
+    <comment>The following are literal names and should not be translated: .NET.
+{0} - The name of the .NET runtime, such as CoreCLR or NativeAOT.</comment>
+  </data>
   <data name="XA4241" xml:space="preserve">
     <value>Java dependency '{0}' is not satisfied.</value>
     <comment>The following are literal names and should not be translated: Java.

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

@@ -553,6 +553,11 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
       FormatArguments="AndroidFastDeploymentType;9"
       Condition=" '$(AndroidFastDeploymentType)' != '' "
   />
+  <AndroidWarning Code="XA1040"
+      ResourceName="XA1040"
+      FormatArguments="$(_AndroidRuntime)"
+      Condition=" '$(_AndroidRuntime)' != 'MonoVM' and '$(EnablePreviewFeatures)' != 'true' "
+  />
 </Target>
 
 <Target Name="_CheckNonIdealConfigurations"