Add support for writing android:roundIcon to Android manifest (#162)

Context: xamarin/XamarinVS#12895

This change is necessary for enabling adaptive icon support in the Android Manifest property page.

It introduces a new attribute `android:roundIcon`.

Co-authored-by: Jonathan Peppers <[email protected]>

Author: japarson

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

@@ -150,6 +150,11 @@ public string? ApplicationIcon {
 			set { application.SetAttributeValue (aNS + "icon", NullIfEmpty (value)); }
 		}
 
+		public string? ApplicationRoundIcon {
+			get { return (string?) application.Attribute (aNS + "roundIcon");  }
+			set { application.SetAttributeValue (aNS + "roundIcon", NullIfEmpty (value)); }
+		}
+
 		public string? ApplicationTheme {
 			get { return (string?) application.Attribute (aNS + "theme"); }
 			set { application.SetAttributeValue (aNS + "theme", NullIfEmpty (value)); }