Update OperatingSystem.IsIOS() docs to mention MacCatalyst (#7781)

IsIOS() also returns true on MacCatalyst since dotnet/runtime@14854e2, update the docs to clarify that.

Author: akoeplinger

xml/System/OperatingSystem.xml

@@ -449,9 +449,9 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>Indicates whether the current application is running on iOS.</summary>
+        <summary>Indicates whether the current application is running on iOS or MacCatalyst.</summary>
         <returns>
-          <see langword="true" /> if the current application is running on iOS; <see langword="false" /> otherwise.</returns>
+          <see langword="true" /> if the current application is running on iOS or MacCatalyst; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -491,9 +491,9 @@
         <param name="major">The major release number.</param>
         <param name="minor">The minor release number.</param>
         <param name="build">The build release number.</param>
-        <summary>Checks if the iOS version (returned by <c>libobjc.get_operatingSystemVersion</c>) is greater than or equal to the specified version. This method can be used to guard APIs that were added in the specified iOS version.</summary>
+        <summary>Checks if the iOS/MacCatalyst version (returned by <c>libobjc.get_operatingSystemVersion</c>) is greater than or equal to the specified version. This method can be used to guard APIs that were added in the specified iOS version.</summary>
         <returns>
-          <see langword="true" /> if the current application is running on an iOS version that is at least what was specified in the parameters; <see langword="false" /> otherwise.</returns>
+          <see langword="true" /> if the current application is running on an iOS/MacCatalyst version that is at least what was specified in the parameters; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>