[CodeCompletion] Implement .Type completion in expression context

[rintaro]

rdar://problem/22072865

[rintaro]

@swift-ci Please smoke test

[slavapestov]

Foo.Type is not valid in expression context. Foo.Type.self is valid, but that creates a meta-metatype which is rare.

However if you're going to complete Foo.Type, please also add Foo.Protocol where foo is a protocol (but again, that's a type term not an expression term).

[rintaro]

Foo.Type is not valid in expression context. Foo.Type.self is valid, but that creates a meta-metatype which is rare.

Because .self is not the only possible suffix to Foo.Type in expression context (e.g. Foo.Type.Type.self), we should not complete .Type.self at once.

However if you're going to complete Foo.Type, please also add Foo.Protocol where foo is a protocol (but again, that's a type term not an expression term).

Fair enough. I've implemented .Protocol completion for both type and expression context.

[rintaro]

@swift-ci Please smoke test