swift

a38c3edc - [CSSimplify] Rework diagnostic handling in `matchExistentialTypes`

[CSSimplify] Rework diagnostic handling in `matchExistentialTypes` It's common for existential matching to happen as part of a larger type matching context i.e. generic arguments, optionals, compositions etc, function types etc. All such cases should be handled higher up, so the diagnostic itself can produce a complete type and pin-point problematic locations. `MissingConformance` cannot be a fallback either because it handles a narrow set of cases, so the matching should fail instead. Resolves: rdar://132432786