BridgeJS: Resolve qualified types relative to lexical scope

[krodak]

Summary

BridgeJS passed qualified type references directly to root lookup. Unlike unqualified identifiers, paths such as Shelf.Divider never searched the enclosing lexical scope, so valid APIs in extensions were diagnosed as unsupported and omitted from the generated bindings.

This applies the existing innermost-to-outermost lookup to the complete qualified path. Extension declarations still resolve their own target from the root scope, while references inside the extension body use the extension's lexical scope.

Closes #805.

Problematic case

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

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

Before, both appearances of Shelf.Divider produced Unsupported type 'Shelf.Divider'. After, the method is exported with the Swift-resolved path:

export interface Library {
    divider(value: Library.Shelf.Divider): Library.Shelf.Divider;
}

Fix

• Apply lexical lookup to both IdentifierTypeSyntax and MemberTypeSyntax
• Keep extension targets root-qualified so an extension cannot resolve into its own member scope
• Cover relative paths and the extension-target shadowing case in codegen and linker snapshots

Test plan

• BridgeJS plugin tests and snapshots with swift-syntax 600, 601, 602, and 603
• Generated TypeScript declaration validation
• AoT binding regeneration

[wfltaylor]

Thanks!