Add API 29 and 30 to KnownVersions

Context: dotnet/android#4873

Although this is related to xamarin-android#4873, it is not the full fix. We probably should list the missing versions here anyway, though.

Author: jonathanpeppers

src/Xamarin.Android.Tools.AndroidSdk/AndroidVersions.cs

@@ -173,6 +173,10 @@ static bool MatchesId (AndroidVersion version, string id)
 			new AndroidVersion (28, "9.0",   "Pie") {
 				AlternateIds = new[]{ "P" },
 			},
+			new AndroidVersion (29, "10.0",  "Android X") {
+				AlternateIds = new[]{ "Q" },
+			},
+			new AndroidVersion (30, "11.0",   "R"),
 		};
 	}