[CoreMedia] Improve CMFormatDescription.SubType properties. Fixes #23217. (#23262)

Any CMPixelFormat value is also a valid CMVideoCodecType value, so duplicate
the values in CMPixelFormat into CMVideoCodecType.

This helps discovery/intellisense.

Also add a CMMediaSubType enum that mirrors the Swift type with the same name, which can be used to improve discovery/intellisense as well.

Additionally, fix a few other issues as well.

Fixes #23217.

Author: rolfbjarne

src/AudioToolbox/AudioType.cs

@@ -48,8 +48,14 @@ public enum AudioFormatType : uint { // UInt32 in AudioStreamBasicDescription --
 		LinearPCM = 0x6c70636d,
 		/// <summary>AC-3  codec.</summary>
 		AC3 = 0x61632d33,
+#if !XAMCORE_5_0
 		/// <summary>CAC-3 codec.</summary>
+		[Obsolete ("Use 'AC3_60958' instead.")]
+		[EditorBrowsable (EditorBrowsableState.Never)]
 		CAC3 = 0x63616333,
+#endif
+		/// <summary>The AC-3 codec, packaged to be compliant with an IEC 60958-compliant digital audio interface.</summary>
+		AC3_60958 = 0x63616333, // 'cac3'
 		/// <summary>Apple's IMA 4:1 ADPCM codec.</summary>
 		AppleIMA4 = 0x696d6134,
 		/// <summary>MPEG-4 AAC codec.</summary>
@@ -140,6 +146,8 @@ public enum AudioFormatType : uint { // UInt32 in AudioStreamBasicDescription --
 		[SupportedOSPlatform ("tvos18.0")]
 		[SupportedOSPlatform ("maccatalyst18.0")]
 		Apac = 0x61706163, // 'apac'
+
+		// any new entries here might need new entries in the CMMediaSubType enum as well
 	}
 
 	/// <summary>Flags describing the stream in the <see cref="AudioToolbox.AudioStreamBasicDescription" />.</summary>