Tests: rename the `generator` files/folders to `generator_interpreter`

[agarny]

This is to be done once issue #1218 has been addressed. For that issue, we want to rely on our generator tests (to ensure that we cover the same cases for our interpreter). This means we should then rename those generator files/folders to generator_interpreter so that it's clear that they are for both our generator and interpreter, and not only our generator.

We could do it as part of issue #1218 but then we would end up with hundreds of files being added/deleted, making the reviewing process unnecessarily difficult. By doing this in a dedicated issue, the reviewing process will very easy since no new functionality will be added. So, as long as the tests pass, we will be all good.