refactor(tvix/eval): refactor locals to use an enum for phantoms r/4754

Instead of using sentinel values and an additional bool, this tracks
the identifier of a local as an enum that is either a statically known
name, or a phantom.

To make this work correctly some more locals related logic has been
encapsulated in the `scope` module, which is a good thing (that's the
goal).

Phantom values are now not initialised by default, but the only
current call site of phantoms (`with` expression compilation) performs
the initialisation right away.

This commit changes no actual functionality right now, but paves the
way for fixing an issue related to `let` bodies.

Change-Id: I679f93a59a4daeacfe40f4012263cfb7bc05034e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6421
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

0 files changed, 0 insertions, 0 deletions