When a witness is part of a `@preconcurrency` conformance, suppress
Sendable checking for that witness because we assume that the caller is
correctly invoking this witness from within the right isolation
domain. This property is dynamically checked.
Fixes https://github.com/apple/swift/issues/74057.
When diagnosing a case where an actor-isolated witness cannot satisfy
a non-isolated requirement, also suggest that the conformance could be
annotated with `@preconcurrency`.
Suppress warnings/errors when actor isolated synchroneous witness
is matched against `@preconcurrency` conformance requirement.
Witness thunk assumes isolation of the witness but instead of a
hop to its executor it would emit a runtime check to make sure
that its always called from the expected context.
