[4.2][CodeComplete] Fix crasher when completing inout IUO variable

[rintaro]

Cherry-pick of #17926 reviewed by @rudkx

• Explaination: When code-completion tries to complete values, it annotates them with their types. Previously when completing inout arguments with IUO type, it used to crash. That was because there's wrong assumption that IUO types are always OptionalType. However, for inout case, it's actually a InOutType with underlying OptionalType. In this change, use ASTPrinter facility which correctly handles such case.
• Scope: Affects completing inout values with IUO. e.g. func fn(arg: inout Int!) { ... }
• Issue: rdar://problem/40956846
• Risk: Low. ASTPrinter's type printing is well tested.
• Testing: Added regression test cases.
• Reviewed By: Mark Lacey ([CodeComplete] Fix crasher when completing inout IUO variable #17926)

[rintaro]

@swift-ci Please test

[rintaro]

@swift-ci Please nominate