Substitution into a generic function type produces non-canonical
generic signatures. This functionality should either be removed or be
completely rewritten to properly use the GenericSignatureBuilder. For
now, disable this one client's unsafe use of it.
This does regression code-completion results slightly, where we were
depending on OverrideFilteringConsumer's behavior to filter out some
redundant results. I've captured the work to fix this properly in
rdar://problem/31245556.
* If "required" or "convenience" is specified, emit only initializers
* If "final" or "open" is specified, don't emit initializers or typealias
* If "typealias" is specified, emit only associated type implementation
* Emit "override" or "required" modifier for initializers
* Emit access modifier for initializers
* Emit designated initializers even if "override" is specified
* Don't emit inheritance clause for associated type implentation
