[SR-15956] [cxx-interop] Swift's type checking doesn't know how to deal with calling functions bound to inline namespace enum

[hyp]

Previous ID	SR-15956
Radar	None
Original Reporter	@hyp
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug, CxxInterop
Assignee	None
Priority	Medium

md5: 3aa3cef7c3ca75618957485c6518bced

Issue Description:

There’s an issue with the Swift’s type checker when invoking functions from the inline namespace.

E.g.
```
namespace X {
inline namespace Y {
void test();

struct other {};
}
}
```

```
import X

extension X.other {
var s: String { return “” }
}

func test() {
X.test() // error here.
}

func test2(_ x: X.other) {
let s = x.s // error here.
}
```

See: https://github.com/apple/swift/blob/main/test/Interop/Cxx/namespace/inline-namespace-function-call-broken.swift