BridgeJS: Resolve qualified type references relative to extension scope #805

BridgeJS resolves unqualified type references relative to their lexical scope, but qualified relative names such as Shelf.Divider are currently treated as root-qualified.

For example:

@JS class Library {
    @JS struct Shelf {
        @JS struct Divider {
            @JS init() {}
        }
    }
}

extension Library {
    @JS func divider(_ value: Shelf.Divider) -> Shelf.Divider {
        value
    }
}

Swift resolves Shelf.Divider as Library.Shelf.Divider. BridgeJS instead looks for a root-level Shelf.Divider, then silently omits divider(_:) from the generated skeleton.

The same behavior exists before #803, although extension-nested types make it easier to run into. MemberTypeSyntax should search from the innermost lexical scope before falling back to a root-qualified path, matching the existing behavior for IdentifierTypeSyntax.