[One .NET] fix $(ApplicationId) and //manifest@package at the same time

Fixes: #6302

If you try to use both `$(ApplicationId)` and `@package` in
`AndroidManifest.xml` at the same time, you hit errors during
deployment:

    Xamarin.Android.Common.Debugging.targets(611,5): error XA0132: The package was not installed. Please check you do not have it installed under any other user.
    If the package does show up on the device, try manually uninstalling it then try again.
    You should be able to uninstall the app via the Settings app on the device.

From the spec, the `AndroidManifest.xml` is *supposed* to be preferred.

I found the `<GetAndroidPackageName/>` MSBuild task is accidentally
preferring the `$(ApplicationId)` MSBuild property. I reordered the
logic and only use the property when no value is found in the
`AndroidManifest.xml`.

I could reproduce the issue in a test, which now passes.

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

@@ -49,23 +49,23 @@ public class GetAndroidPackageName : AndroidTask
 
 		public override bool RunTask ()
 		{
-			if (!string.IsNullOrEmpty (PackageName)) {
-				PackageName = AndroidAppManifest.CanonicalizePackageName (PackageName);
-			} else if (!string.IsNullOrEmpty (ManifestFile) && File.Exists (ManifestFile)) {
+			if (!string.IsNullOrEmpty (ManifestFile) && File.Exists (ManifestFile)) {
 				using var stream = File.OpenRead (ManifestFile);
 				using var reader = XmlReader.Create (stream);
 				if (reader.MoveToContent () == XmlNodeType.Element) {
 					var package = reader.GetAttribute ("package");
 					if (!string.IsNullOrEmpty (package)) {
-						package = ManifestDocument.ReplacePlaceholders (ManifestPlaceholders, package);
-						PackageName = AndroidAppManifest.CanonicalizePackageName (package);
+						PackageName = ManifestDocument.ReplacePlaceholders (ManifestPlaceholders, package);
 					}
 				}
 			}
 
-			// If we don't have a manifest, default to using the assembly name
-			// If the assembly doesn't have a period in it, duplicate it so it does
-			if (string.IsNullOrEmpty (PackageName)) {
+			if (!string.IsNullOrEmpty (PackageName)) {
+				// PackageName may be passed in via $(ApplicationId) and missing from AndroidManifest.xml
+				PackageName = AndroidAppManifest.CanonicalizePackageName (PackageName);
+			} else {
+				// If we don't have a manifest, default to using the assembly name
+				// If the assembly doesn't have a period in it, duplicate it so it does
 				PackageName = AndroidAppManifest.CanonicalizePackageName (AssemblyName);
 			}
 

tests/MSBuildDeviceIntegration/Tests/InstallAndRunTests.cs

@@ -626,5 +626,29 @@ public void RunWithInterpreterEnabled ([Values (false, true)] bool isRelease)
 			Assert.IsTrue (didStart, "Activity should have started.");
 		}
 
+		[Test]
+		public void SingleProject_ApplicationId ()
+		{
+			AssertHasDevices ();
+
+			proj = new XamarinAndroidApplicationProject ();
+			proj.SetProperty ("ApplicationId", "com.i.should.get.overridden.by.the.manifest");
+
+			var abis = new string [] { "armeabi-v7a", "arm64-v8a", "x86", "x86_64" };
+			proj.SetAndroidSupportedAbis (abis);
+			builder = CreateApkBuilder ();
+			Assert.IsTrue (builder.Install (proj), "Install should have succeeded.");
+
+			if (Builder.UseDotNet)
+				Assert.True (builder.RunTarget (proj, "Run"), "Project should have run.");
+			else if (CommercialBuildAvailable)
+				Assert.True (builder.RunTarget (proj, "_Run"), "Project should have run.");
+			else
+				AdbStartActivity ($"{proj.PackageName}/{proj.JavaPackageName}.MainActivity");
+
+			var didStart = WaitForActivityToStart (proj.PackageName, "MainActivity",
+				Path.Combine (Root, builder.ProjectDirectory, "startup-logcat.log"));
+			Assert.IsTrue (didStart, "Activity should have started.");
+		}
 	}
 }