winemac: Put clipboard formats synthesized from other standard clipboard formats at the end of the list.

This makes sure that the formats are enumerated in a consistent order.

winemac: Cache the "natural" clipboard format entry associated with synthesized built-in entries at startup.

New clipboard formats had been registered for them, but that was pointless.
No Windows app would ever expect or make use of such clipboard formats or the
associated pasteboard data.

winemac: Add support for a "Decorated" registry setting to control whether windows get Mac-style decorations.