swift234

Continue tidying up Initialization, NFC:
 - Privatize "kind" in the base Initialization class.
 - Simplify canForwardInBranch() to just isSingleBuffer().
   There is only one client of it (which avoids emitting the
   formation of an optional temporary) and the only cases we're
   dropping is for "_" patterns and single element tuple patterns,
   which are not worth optimizing for.
 - Change getSubInitializationsForTuple() into a virtual method
   since it has wildly different behavior based on the subclass and
   requires otherwise private implementation details of those subclasses
   to implement it.
 - Simplify subclasses based on these changes.



Swift SVN r27463