Revert "[generator] Remove androidx.annotation from Annotation names (dotnet#882)"

Partially revert commit 1e8f513.

Context: dotnet#885

The problem with commit 1e8f513 is that the change to the
`AnnotationData` constructor broke the xamarin-android
build, introducing API Compatibility errors in `Mono.Android.dll`:

	…/src/Mono.Android/Mono.Android.targets(247,5): error : CompatApi command: $HOME/.nuget/packages/microsoft.dotnet.apicompat/5.0.0-beta.20181.7/tools/net472/Microsoft.DotNet.ApiCompat.exe "…/bin/Debug/lib/xamarin.android/xbuild-frameworks/MonoAndroid/v4.4.87/Mono.Android.dll" -i "…/bin/Debug/lib/xamarin.android/xbuild-frameworks/MonoAndroid/v5.0" --allow-default-interface-methods --baseline "…/tests/api-compatibility/acceptable-breakages-v5.0.txt" --validate-baseline --exclude-attributes "…/tests/api-compatibility/api-compat-exclude-attributes.txt"
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CheckApiCompatibility found nonacceptable Api breakages for ApiLevel: v5.0.
	…/src/Mono.Android/Mono.Android.targets(247,5): error : Compat issues with assembly Mono.Android:
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CannotChangeAttribute : Attribute 'Android.Runtime.RequiresPermissionAttribute' on 'Android.Net.ConnectivityManager.GetNetworkInfo(Android.Net.ConnectivityType)' changed from '[RequiresPermissionAttribute("quot;android.permission.ACCESS_NETWORK_STATE&quot")]' in the contract to '[RequiresPermissionAttribute("quot;android.permission.ACCESS_NETWORK_STATE&quot")]' in the implementation.
	…/src/Mono.Android/Mono.Android.targets(247,5): error : CannotChangeAttribute : Attribute 'Android.Runtime.RequiresPermissionAttribute' on 'Android.OS.Vibrator.Vibrate(System.Int64[], System.Int32)' changed from '[RequiresPermissionAttribute("quot;android.permission.VIBRATE&quot")]' in the contract to '[RequiresPermissionAttribute("quot;android.permission.VIBRATE&quot")]' in the implementation.
	…/src/Mono.Android/Mono.Android.targets(247,5): error : Total Issues: 2

See Issue dotnet#885 for more details and discussion.  TL;DR: 1e8f513
allowed `androidx.annotation.RequiresPermission` to be surfaced as
`[Android.Runtime.RequiresPermission]` custom attributes, and in
doing so surfaced a pre-existing issue wherein the same
`[RequiresPermission]` could be present multiple times with the same
constructor values, which typically isn't desirable:

	namespace Android.OS {
	    public abstract partial class Vibrator : Java.Lang.Object {
	        [global::Android.Runtime.RequiresPermission ("quot;android.permission.VIBRATE&quot")]
		[global::Android.Runtime.RequiresPermission ("quot;android.permission.VIBRATE&quot")]
	        public abstract void Vibrate (long milliseconds);
	    }
	}

How and why this is happening isn't currently understood.

In the meantime, revert the `AnnotationData` changes in commit
1e8f513 so that we can bump Java.Interop within xamarin-android.

Author: jonpryor

src/Xamarin.Android.Tools.AnnotationSupport/Objects/AnnotationData.cs

@@ -7,20 +7,13 @@ namespace Xamarin.AndroidTools.AnnotationSupport
 {
 	public class AnnotationData : AnnotationObject
 	{
-		static readonly string[] Prefixes = new[] {
-			"android.support.annotation.",
-			"androidx.annotation.",
-		};
 		public AnnotationData (XElement e)
 		{
 			var a = e.Attribute ("name");
 			Name = a == null ? null : a.Value;
-			foreach (var predef in Prefixes) {
-				if (!Name.StartsWith (predef, StringComparison.Ordinal))
-					continue;
+			string predef = "android.support.annotation.";
+			if (Name.StartsWith (predef, StringComparison.Ordinal))
 				Name = Name.Substring (predef.Length);
-				break;
-			}
 			Values = e.Elements ("val").Select (c => new AnnotationValue (c)).ToArray ();
 		}