Add test for difference between export * as x from and import * as x; export { x }

[nicolo-ribaudo]

This is a test for the difference described in tc39/ecma262#3710.

TL;DR

• export { foo } from "mod" and import { foo } from "mod"; export { foo } are equivalent: they both propagate the binding, so when both re-exported with export * from they do not cause ambiguity.
• export * as foo from "mod" and import * as foo from "mod"; export { foo } are not equivalent: the second one introduces a new binding, causing ambiguity. It would be unambiguous if both were doing export * as foo from "mod". It's still be ambiguous (two bindings) if both were doing import * as foo from "mod"; export { foo }

The first commit just moves the tests related to binding ambiguity to a single folder, so that it's easier to tell what is already tested.

[nicolo-ribaudo]

SM/JSC pass all the tests, while V8/engine262/XS fail test/language/module-code/ambiguous-export-bindings/namespace-unambiguous-if-export-start-as-from.js

[nicolo-ribaudo]

Marking as draft because I plan to present something related to this in plenary.