generator: generate platform attributes all over

Cleaner than before by encapsulating in a PrintPlatformAttributes
method. This ensures attributes are generated on types, methods,
properties, and property getter and setter methods.
Tests: skip based on MemberInfo attributes at all levels

This allows test implementations to hook in and skip
tests against MemberInfos that have or do not have
certain attributes meeting some criteria.

Used to ensure MountainLion APIs do not attempt to be
tested on Lion or older, etc.