When "optional type" is a hole the simplification logic has to
simplify "object type" and mark all of its unresolved components
are potential holes, otherwise hole propagation won't work since
sometimes there is no other contextual information for such types
but "optional type".
Resolves: rdar://117871338
This commit changes fixit messages from a question/suggestion to an
imperative message for protocol conformances and switch-case. Addresses
https://github.com/apple/swift/issues/67510.
1. Make sure the actions taken by fixits are reflected in diagnostics messages.
2. Issue missing cases diagnostics at the start of the switch statement instead of its end.
3. Use <#code#> instead of <#Code#> in the stub.
