[bgen] Add iOSAttribute and MacAttribute to the binding attributes. (#23806)

This way third-party libraries can use the [iOS] and [Mac] attributes ([TV]
and [MacCatalyst] are already available).

This also means we can remove some of our legacy/special COREBUILD-only code.

Author: rolfbjarne

src/ObjCRuntime/PlatformAvailability.cs

@@ -1217,6 +1217,32 @@ public MacCatalystAttribute (byte major, byte minor, byte subminor)
 	}
 }
 
+[AttributeUsage (AttributeTargets.All, AllowMultiple = false)]
+public sealed class MacAttribute : IntroducedAttribute {
+	public MacAttribute (byte major, byte minor)
+		: base (PlatformName.MacOSX, (int) major, (int) minor)
+	{
+	}
+
+	public MacAttribute (byte major, byte minor, byte subminor)
+		: base (PlatformName.MacOSX, (int) major, (int) minor, subminor)
+	{
+	}
+}
+
+[AttributeUsage (AttributeTargets.All, AllowMultiple = false)]
+public sealed class iOSAttribute : IntroducedAttribute {
+	public iOSAttribute (byte major, byte minor)
+		: base (PlatformName.iOS, (int) major, (int) minor)
+	{
+	}
+
+	public iOSAttribute (byte major, byte minor, byte subminor)
+		: base (PlatformName.iOS, (int) major, (int) minor, subminor)
+	{
+	}
+}
+
 [AttributeUsage (AttributeTargets.All, AllowMultiple = false)]
 public sealed class NoMacAttribute : UnavailableAttribute {
 	public NoMacAttribute ()

src/ObjCRuntime/PlatformAvailability2.cs

@@ -59,7 +59,6 @@
     <Compile Include="$(RepositoryPath)\src\ObjCRuntime\LinkWithAttribute.cs" />
     <Compile Include="$(RepositoryPath)\src\ObjCRuntime\NativeAttribute.cs" />
     <Compile Include="$(RepositoryPath)\src\ObjCRuntime\NativeNameAttribute.cs" />
-    <Compile Include="$(RepositoryPath)\src\ObjCRuntime\PlatformAvailability2.cs" />
     <Compile Include="$(RepositoryPath)\src\ObjCRuntime\Registrar.core.cs" />
     <Compile Include="$(RepositoryPath)\src\ObjCRuntime\RequiresSuperAttribute.cs" />
     <Compile Include="$(RepositoryPath)\tools\common\Execution.cs">

src/bgen/Attributes.cs

@@ -1845,8 +1845,6 @@ SHARED_CORE_SOURCES = \
 	ObjCRuntime/TransientString.cs \
 	ObjCRuntime/NFloat.cs \
 	ObjCRuntime/ObsoleteConstants.cs \
-	ObjCRuntime/PlatformAvailability.cs \
-	ObjCRuntime/PlatformAvailability2.cs \
 	ObjCRuntime/Protocol.cs \
 	ObjCRuntime/Registrar.core.cs \
 	ObjCRuntime/RequiresSuperAttribute.cs \

src/bgen/bgen.csproj

@@ -1542,6 +1542,18 @@ public void UnderlyingFieldType (Profile profile)
 			BuildFile (profile, true, true, "tests/underlyingfieldtype.cs");
 		}
 
+		[Test]
+		[TestCase (Profile.iOS)]
+		[TestCase (Profile.tvOS)]
+		[TestCase (Profile.MacCatalyst)]
+		[TestCase (Profile.macOSMobile)]
+		public void AvailabilityAttributes (Profile profile)
+		{
+			Configuration.IgnoreIfIgnoredPlatform (profile.AsPlatform ());
+			var bgen = BuildFile (profile, "tests/availability-attributes.cs");
+			bgen.AssertNoWarnings ();
+		}
+
 		[Test]
 		[TestCase (Profile.iOS)]
 		public void DelegatesWithNullableReturnType (Profile profile)