[alpha.webkit.NoUnretainedMemberChecker] Recognize NS_REQUIRES_PROPERTY_DEFINITIONS (#143408)
Allow @property of a raw pointer when NS_REQUIRES_PROPERTY_DEFINITIONS
is specified on the interface since such an interface does not
automatically synthesize raw pointer ivars.
Also emit a warning for @property(assign) and
@property(unsafe_unretained) under ARC as well as when explicitly
synthesizing a unsafe raw pointer property.