swift234

Fix <rdar://problem/23272739> Poor diagnostic due to contextual constraint
Previously we erroneously complained:
  error: cannot invoke 'contains' with an argument list of type '(String)'
now we correctly complain:
  error: unexpected non-void return value in void function

This enhances CSDiags to use "getTypeOfMember" when analyzing method
candidates that are applied to a known base type.  Using it allows us to
substitute information about the base, resolving archetypes that exist in
subsequent argument positions.  In the testcase, this means that we use
information about Set<String> to know that the argument to "contains" is a
String.

This allows us to generate much better diagnostics in some cases, and works
around some limitations in the existing stuff for handling unresolved
archetypes.  One unfortunate change is the notes in Misc/misc_diagnostics.swift.
Because we don't track argument lists very well, we are flattening an argument
list that is actually ((Int,Int)) into (Int, Int) so we get a bogus looking
diagnostic.  This was possible before this patch though, it is just one
more case that triggers the issue.