swift234

Pattern processing cleanups, NFC:

Introduce a new Pattern::forEachVariable that takes a lambda and iterates
over all the variables encompassed by the pattern (the ones found by
collectVariables) and runs the lambda on it.

Use this to implement collectVariables, so we only have one copy of the code.

Convert several places to use this, removing a bunch of duplicated code for
walking the pattern structure and extracting decls.

Convert a few uses of collectVariables to forEachVariable, leading to more
clear code without a temporary smallvector.

Remove simplifyPatternTypes in CSApply.cpp, which is dead.



Swift SVN r13545