[tests] verify trimmer warnings where appropriate (#9076)

One change we need in the Android workload is to make sure that
trimmer warnings are displayed if a project sets `$(IsAotCompatible)`.
Customers would likely want this set for all platforms if they are
using NativeAOT on iOS or MacCatalyst.

I also wrote a test with somewhat complicated parameters to verify
we get warnings.

First, I can create a warning for both `IL2055` and `IL3050`:

    // Member field
    Type type = typeof (List<>);
    // ...
    // Later in OnCreate
    Console.WriteLine (type.MakeGenericType (typeof (object)));

The combinations of tests are:

| Configuration | Property                           | Warning(s)        |
| ------------- | ---------------------------------- | ----------------- |
| Debug         | (defaults)                         | None              |
| Release       | (defaults)                         | None              |
| Debug         | TrimMode=full                      | None              |
| Release       | TrimMode=full                      | IL2055(2)         |
| Release       | SuppressTrimAnalysisWarnings=false | IL2055(2)         |
| Debug         | IsAotCompatible=true               | IL2055, IL3050    |
| Release       | IsAotCompatible=false              | IL2055(2), IL3050 |

Some of the cases receive duplicate warnings, but this is expected as
the same behavior occurs in the simplest case:

* `dotnet new console`
* Add the above code to `Program.cs`
* `dotnet publish -c Release -r win-x64 -p:PublishAot=true`
* Receive warnings from both the Roslyn analyzer and ILC (NativeAOT compiler)

In a future PR, I might try to "fix" the duplicate warnings.

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.DefaultProperties.targets

@@ -85,7 +85,7 @@
     <!-- For compat with user code not marked trimmable, only trim opt-in by default. -->
     <TrimMode Condition=" '$(TrimMode)' == '' and '$(AndroidLinkMode)' == 'Full' ">full</TrimMode>
 		<TrimMode Condition="'$(TrimMode)' == ''">partial</TrimMode>
-    <SuppressTrimAnalysisWarnings Condition=" '$(SuppressTrimAnalysisWarnings)' == '' and '$(TrimMode)' == 'full' ">false</SuppressTrimAnalysisWarnings>
+    <SuppressTrimAnalysisWarnings Condition=" '$(SuppressTrimAnalysisWarnings)' == '' and ('$(TrimMode)' == 'full' or '$(IsAotCompatible)' == 'true') ">false</SuppressTrimAnalysisWarnings>
     <SuppressTrimAnalysisWarnings Condition=" '$(SuppressTrimAnalysisWarnings)' == '' ">true</SuppressTrimAnalysisWarnings>
     <!-- Prefer $(RuntimeIdentifiers) plural -->
     <RuntimeIdentifiers Condition=" '$(RuntimeIdentifier)' == '' And '$(RuntimeIdentifiers)' == '' ">android-arm;android-arm64;android-x86;android-x64</RuntimeIdentifiers>

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest2.cs

@@ -269,6 +269,48 @@ public void BuildHasNoWarnings (bool isRelease, bool xamarinForms, bool multidex
 			}
 		}
 
+		[Test]
+		[TestCase ("", new string [0], false)]
+		[TestCase ("", new string [0], true)]
+		[TestCase ("SuppressTrimAnalysisWarnings=false", new string [] { "IL2055" }, true, 2)]
+		[TestCase ("TrimMode=full", new string [0], false)]
+		[TestCase ("TrimMode=full", new string [] { "IL2055" }, true, 2)]
+		[TestCase ("IsAotCompatible=true", new string [] { "IL2055", "IL3050" }, false)]
+		[TestCase ("IsAotCompatible=true", new string [] { "IL2055", "IL3050" }, true, 3)]
+		public void BuildHasTrimmerWarnings (string properties, string [] codes, bool isRelease, int? totalWarnings = null)
+		{
+			var proj = new XamarinAndroidApplicationProject {
+				IsRelease = isRelease,
+			};
+			proj.SetRuntimeIdentifier ("arm64-v8a");
+			proj.MainActivity = proj.DefaultMainActivity
+				.Replace ("//${FIELDS}", "Type type = typeof (List<>);")
+				.Replace ("//${AFTER_ONCREATE}", "Console.WriteLine (type.MakeGenericType (typeof (object)));");
+			proj.SetProperty ("TrimmerSingleWarn", "false");
+
+			if (!string.IsNullOrEmpty (properties)) {
+				foreach (var property in properties.Split (';')) {
+					int index = property.IndexOf ('=');
+					if (index != -1) {
+						proj.SetProperty (property [..index], property [(index + 1)..]);
+					}
+				}
+			}
+
+			using var b = CreateApkBuilder (Path.Combine ("temp", TestName));
+			Assert.IsTrue (b.Build (proj), "Build should have succeeded.");
+
+			if (codes.Length == 0) {
+				b.AssertHasNoWarnings ();
+			} else {
+				totalWarnings ??= codes.Length;
+				Assert.True (StringAssertEx.ContainsText (b.LastBuildOutput, $"{totalWarnings} Warning(s)"), $"Should receive {totalWarnings} warnings");
+				foreach (var code in codes) {
+					Assert.True (StringAssertEx.ContainsText (b.LastBuildOutput, code), $"Should receive {code} warning");
+				}
+			}
+		}
+
 		[Test]
 		[TestCase ("AndroidFastDeploymentType", "Assemblies", true, false)]
 		[TestCase ("AndroidFastDeploymentType", "Assemblies", false, false)]

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Resources/Base/MainActivity.cs

@@ -13,6 +13,7 @@ namespace ${ROOT_NAMESPACE}
 	[Register ("${JAVA_PACKAGENAME}.MainActivity"), Activity (Label = "${PROJECT_NAME}", MainLauncher = true, Icon = "@drawable/icon")]
 	public class MainActivity : Activity
 	{
+		//${FIELDS}
 		int count = 1;
 
 		protected override void OnCreate (Bundle bundle)

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Resources/DotNet/MainActivity.cs

@@ -4,6 +4,7 @@ namespace ${ROOT_NAMESPACE}
 	[Android.Runtime.Register ("${JAVA_PACKAGENAME}.MainActivity"), Activity (Label = "${PROJECT_NAME}", MainLauncher = true, Icon = "@drawable/icon")]
 	public class MainActivity : Activity
 	{
+		//${FIELDS}
 		int count = 1;
 
 		protected override void OnCreate (Bundle? bundle)