[Sema] Warn about 'Any' to 'any Sendable' override

[angela-laar]

Until Swift 6, warn about overriding Any property in parent class to any Sendable

[angela-laar]

@swift-ci please smoke test

[xedin]

One major drawback of this approach is that it strips concurrency annotations from both sides which means that override with concurrency annotations would match against parent without annotation(s) in the same position which is not the case for witness matching today. For example:

protocol P {
    @preconcurrency func test(_: Any)
}

struct S : P {
    func test(_: any Sendable) {}
}

Produces the following error:

error: type 'S' does not conform to protocol 'P'
1 | protocol P {
2 |     @preconcurrency func test(_: Any)
  |                          `- note: protocol requires function 'test' with type '(Any) -> ()'; add a stub for conformance
3 | }
4 |
5 | struct S : P {
  |        `- error: type 'S' does not conform to protocol 'P'
6 |     func test(_: any Sendable) {}
  |          `- note: candidate has non-matching type '(any Sendable) -> ()'
7 | }

Taking a step back here, at line https://github.com/apple/swift/pull/73543/files#diff-149ea7785899898da39642522a1b7d555757f96e8a3d53f045f9ae80e04c361bR1208 the types are checked for exact match which means that it should be possible to set a new flag based on whether base is marked as preconcurrency or not before attempting propertyTy->matches(parentPropertyCanTy, options) and handle it inside matches but that would make it harder to deal with check that compares object types (that happens right under this one) and diagnose sendability mismatches as warnings, so I'd like to propose a combination:

1. We still ran if (!propertyTy->matches(parentPropertyCanTy, options)) first;
2. If that fails we add TypeMatchFlags::IgnoreSendability and TypeMatchFlags::IgnoreFunctionSendability and re-run matches
3. If propertyTy->matches(parentPropertyCanTy, options) returns true we set mismatchedOnSendability = true; this would allow us diagnose sendability mismatch and avoid dealing with optionality mismatches diagnosed in https://github.com/apple/swift/pull/73543/files#diff-149ea7785899898da39642522a1b7d555757f96e8a3d53f045f9ae80e04c361bR1304
4. Change matches to handle the case where any Sendable is matched against Any and ignore it if IgnoreSendability flag is set.

• This means that matches has to be a bit more work by walking into tuples and collections but only if the flag is set.

[xedin]

I left a comment about adding more tests with different combinations of attributes and any Sendable use in the previous PR.

[xedin]

This change is not technically tied for this PR since matching happens on canonical types, you can land this separately.