Support the optional property attributes in mtl_copyPropertyAttributes

[zhaorui]

As of macOS 14.4, Xcode 15, optional property such as a debugDescription now is encoded with '?'
Let's take a look the example of debugDescription.

@protocol NSObject
@optional
@property (readonly, copy) NSString *debugDescription;
@end

Its property description is T@"NSString",?,R,C, since the '?' is unknown to Mantle, Here comes a lot of log like:

ERROR: Unrecognized attribute string flag '?' in attribute string "T@"NSString",?,R,C" for property debugDescription

I suggest Mantle to support this optional attribute of property for suppressing these log.

Declared Properties

[github-actions]

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