`TypeChecker::containsProtocol` shouldn't propagate user-provided
`allowMissing` to existential superclass check because the type
could be `& Sendable` and `allowMissing` propagation would result
in invalid builtin conformance returned for a non-conforming
superclass.
This means that:
1. In test cases where minimal is the default (swift 5 without
-warn-concurrency), I added RUN lines for targeted, complete, and complete +
sns.
2. In test cases where complete is the default (swift 6, -warn-concurrency,
specified complete with -strict-concurrency), I added a send non-sendable run
line.
In each of these cases, I added additional expected-* lines as appropriate so
the tests can compile in each mode successfully.
When performing conversions to an existential that involves Sendable,
introducing missing conformances as needed to allow the type-check to
succeed and then (later) they'll be diagnosed appropriately.
Fixes rdar://89992095.
