swift234

[stdlib] BridgeStorage optimizations

Stop trafficking in optionals and using checked arithmetic; the
optimizer doesn't like that.  Also drop a needless cast, fix up some
names, and accept a native 2nd argument.  Only classes imported from
ObjC actually have non-native refcounting, and we don't really care
about enforcing that for the 2nd argument.  It's just expected to be a
possibly-non-native class.

Swift SVN r23396