Expose PropertyInstruction's getPropertyArguments()

[rcjsuen]

In c7416ab#diff-0bbbf3173979775c0d43c5237a287a4c, we changed PropertyInstruction to not override getArguments() with its own variant for the sake of consistency and changed this variant into a private function named getPropertyArguments().

As this is quite a big change and may cause problems downstream for people that expect PropertyInstruction subclasses to return more "manageable" arguments with getArguments(), we should make getPropertyArguments() public and let anyone downstream change their code to call that instead.