swift234

[Sema] Improve diagnostics for attempt to throw an error *code*

Attempting to throw an error code value, e.g.,

  throw CocoaError.fileNoSuchFileError

is now ill-formed, although it was well-formed prior to the
introduction of NSError bridging (SE-0112). Provide a specialized
diagnostic with a Fix-It to add the appropriate parentheses:

  throw CocoaError(.fileNoSuchFileError)

Fixes rdar://problem/27543121.