When providing code completions for an argument in an Objective-C

When providing code completions for an argument in an Objective-C
message send, e.g.,

  [[NSString alloc] initWithCString:<CC>

look up all of the possible methods and determine the preferred type
for the argument expression based on the type of the corresponding
parameter.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@114379 91177308-0d34-0410-b5e6-96231b3b80d8