Fix @scope shadowing (rewrite using globalThis)

[cknitt]

Fix @scope shadowing (fixes #7478)

Summary

When @scope("URL") is used inside a module named URL, the local module binding shadows the global URL and the JS output calls the wrong object. This PR rewrites the scope base to globalThis.URL when the scope name is shadowed by a local module binding.

Example:

module URL = {
  @val @scope("URL")
  external revokeObjectURL: string => unit = "revokeObjectURL"
}

URL.revokeObjectURL("some url")

Output after this change:

globalThis.URL.revokeObjectURL("some url");

Why this approach

• The problem is shadowing: a local module name hides the intended global scope.
• We only rewrite the scope base when a local binding would shadow it.
• This keeps normal code unchanged and avoids adding globalThis everywhere.

Tests

• tests/tests/src/ExternalScopeShadow.res covers the shadowed scope and module alias case.

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commit: 6888c01

[cristianoc]

Looks good to me.
I assume the generated js is the desired one.

[cknitt]

Yes, JS output is fine.