Remove lowering cruft from ingot/module items

[sbillig]

What was wrong?

Closes #720 (I think; @Y-Nak, are you aware of any other leftorovers?)

The only functional change is that db.set_ingot_modules has been replaced with db.set_ingot_files. The former was a compromise to work with lowered modules. Now the latter will be used by the (imaginary) language server to update the list of files in a project.

How was it fixed?

🧠

To-Do

• OPTIONAL: Update Spec if applicable

• Add entry to the release notes (may forgo for trivial changes)

• Clean up commit history

[codecov-commenter]

Codecov Report

Merging #727 (dd79c53) into master (43b58a8) will increase coverage by 0.27%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master     #727      +/-   ##
==========================================
+ Coverage   81.92%   82.19%   +0.27%     
==========================================
  Files         105      105              
  Lines       11822    11780      -42     
==========================================
- Hits         9685     9683       -2     
+ Misses       2137     2097      -40     

Impacted Files	Coverage Δ
crates/analyzer/src/context.rs	61.66% <ø> (ø)
crates/analyzer/src/db.rs	100.00% <ø> (ø)
crates/analyzer/src/db/queries/functions.rs	61.53% <0.00%> (ø)
crates/analyzer/src/db/queries/module.rs	77.69% <ø> (+0.57%)	⬆️
crates/analyzer/src/errors.rs	79.59% <ø> (ø)
crates/analyzer/src/namespace/scopes.rs	79.41% <ø> (+0.27%)	⬆️
crates/analyzer/src/namespace/types.rs	61.36% <ø> (+2.84%)	⬆️
crates/analyzer/src/traversal/declarations.rs	92.30% <ø> (-0.29%)	⬇️
crates/common/src/files.rs	91.30% <ø> (ø)
crates/parser/src/ast.rs	78.65% <ø> (+0.72%)	⬆️
... and 5 more

---

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[Y-Nak]

Seems nice!

In addition to the changes that you've made, we could remove

fe/crates/analyzer/src/context.rs

Line 380 in 43b58a8

pub var_decl_types: IndexMap<NodeId, Type>,

and

fe/crates/analyzer/src/namespace/scopes.rs

Line 196 in 43b58a8

pub fn add_declaration(&self, node: &Node<ast::TypeDesc>, typ: Type) {

var_decl_types are referred by fe-lowering, but it's no longer used. Also it wrongly stores type annotation spans as its key, instead of variables spans.
So I think it'd be better to remove them in favor of

fe/crates/analyzer/src/context.rs

Line 376 in 43b58a8

pub var_types: IndexMap<NodeId, Type>,

Of course, it's completely fine if you merge this PR as is.
I like mindless work and I'll do it after mering the PR 😄

[sbillig]

var_decl_types are referred by fe-lowering, but it's no longer used.

Gone! I also removed some other dead code, as revealed by https://github.com/est31/warnalyzer

[Y-Nak]

👍
Left one nit.