Improve code completion for Objective-C message sends when the opening

Improve code completion for Objective-C message sends when the opening
'[' is missing. Prior commits improving recovery also improved code
completion beyond the first selector, e.g., at or after the "to" in

  calculator add:x to:y

but not after "calculator". We now provide the same completions for

  calculator <CC>

that we would for

  [calculator <CC>

if "calculator" is an expression whose type is something that can
receive Objective-C messages.

This code completion works for instance and super message sends, but not
class message sends.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@113976 91177308-0d34-0410-b5e6-96231b3b80d8