swift234

Introduce new entry point _arrayBridgeFromObjectiveC for checked T[] -> U[] conversions.

This entry point is used when T is bridged verbatim and U is bridged
non-verbatim. It attempts to bridge each T from Objective-C to a U,
and returns nil if any of the elements cannot be bridged back to a U.

For now, only _convertNSArrayToArray and Array.bridgeFromObjectiveC
depend on this. It will soon be used for checked casts from, e.g.,
AnyObject[] to String[].

This is part of <rdar://problem/16952771> and general array bridging.

Swift SVN r18369