swift234

Completely redesign our AST representation of capturelists.  Formerly,
a capture list hung off the CaptureExpr it was associated with.  This made
sense lexically (since a capture list is nested inside of the closure) but
not semantically.  Semantically, the capture list initializers are evaluated
outside the closure, the variables are bound to those values, then the closure
captures the newly bound values.

To directly represent this, represent captures with a new CaptureListExpr node,
which contains the ClosureExpr inside of it.  This correctly models the semantic
relationship, and makes sure that AST walkers all process the initializers of the
capture list as being *outside* of the closure.

This fixes rdar://19146761 and probably others.


Swift SVN r23756