[SR-14407] ☂️ Inconsistent behavior between sugared types and desugared types

[typesanitizer]

Previous ID	SR-14407
Radar	rdar://problem/75914560
Original Reporter	@typesanitizer
Type	Bug

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 1f5bf4ce7efa520109e613cc3c512109

Sub-Tasks:

• SR-13770 Optional "?" sugar for nested types works within functions but not outside
• SR-13838 S? is not regarded as Optional<S> in "case" expression.

Issue Description:

In certain cases, the compiler has different behavior when a sugared type such as T? is used instead of the desugared type Optional<T>. This Jira is for tracking different issues related to the same failure mode.

[typesanitizer]

@swift-ci create