Speed up indexing by not calling deps_dir for every file

[lukad]

This significantly speeds up indexing on very large codebases.
Brought down indexing time from ~2 hours to ~2 minutes on the project I tested this on.

[scohen]

Well, the reason I made the deps_dir function was to do this, I was mistaken about how anonymous functions are built.
Mea culpa. Two hours is a heck of a run, heck, two minutes is a long indexing run.

How big is your codebase?

[lukad]

15k+ elixir files, so it's no surprise that calling into the remote project for every file has such a big impact.
Anyways, thanks a lot for lexical. It makes working on such a large codebase so much more enjoyable.

[tessi]

for the love of whatever deity you (not) believe in, thank you @lukad for this PR! And lexical in general for being awesome. This is saving my day on the very same humongous codebase 💜