[MetricKit] Add availability attributes to MXMetaData.DictionaryRepresentation. (#17294)

Author: rolfbjarne

src/MetricKit/MXMetaData.cs

@@ -1,4 +1,4 @@
-#if IOS
+#if IOS || __MACCATALYST__
 
 #nullable enable
 
@@ -12,6 +12,15 @@ namespace MetricKit {
 
 	public partial class MXMetaData {
 
+#if NET
+		[SupportedOSPlatform ("ios14.0")]
+		[SupportedOSPlatform ("maccatalyst14.0")]
+		[SupportedOSPlatform ("macos12.0")]
+		[UnsupportedOSPlatform ("tvos")]
+#else
+		[Introduced (PlatformName.iOS, 14, 0)]
+		[Introduced (PlatformName.MacOSX, 12, 0)]
+#endif
 		public virtual NSDictionary DictionaryRepresentation {
 			get {
 				if (SystemVersion.CheckiOS (14,0))