feature: use statements language support

[baszalmstra]

Adds the use of use statements in the code.

✔️ Features

• Parsing of use statements (e.g. use foo::bar::{Bar, Baz})
• Resolve all use statements in all modules
• Errors for unresolved use statement
• Errors for cyclic use statements
• Wildcard use statements
• Proper error for importing a duplicate name

❓ Missing features, but planned

I will create issues for these once this is merged.

• Errors for illegal import statement visibility
• Errors for leaking non-visibile types

❌ Out of scope

• Runtime dependencies (so this is actually not actually usable yet)

Closes #249

[codecov]

Codecov Report

Merging #290 (0fd6ae6) into master (c0185b7) will decrease coverage by 0.61%.
The diff coverage is 80.45%.

@@            Coverage Diff             @@
##           master     #290      +/-   ##
==========================================
- Coverage   81.41%   80.80%   -0.62%     
==========================================
  Files         239      240       +1     
  Lines       14025    14584     +559     
==========================================
+ Hits        11419    11785     +366     
- Misses       2606     2799     +193     

Impacted Files	Coverage Δ
crates/mun_hir/src/item_tree.rs	76.59% <0.00%> (-2.76%)	⬇️
crates/mun_hir/src/item_tree/tests.rs	93.54% <0.00%> (-6.46%)	⬇️
crates/mun_hir/src/module_tree.rs	86.73% <ø> (ø)
crates/mun_syntax/src/lib.rs	63.04% <ø> (ø)
crates/mun_hir/src/item_scope.rs	49.36% <29.62%> (-43.23%)	⬇️
crates/mun_hir/src/visibility.rs	80.64% <50.00%> (-7.36%)	⬇️
crates/mun_hir/src/diagnostics.rs	63.98% <66.66%> (+1.92%)	⬆️
crates/mun_syntax/src/syntax_kind/generated.rs	67.74% <80.00%> (+0.45%)	⬆️
crates/mun_hir/src/package_defs/collector.rs	82.35% <82.12%> (-2.43%)	⬇️
crates/mun_hir/src/item_tree/lower.rs	95.41% <84.61%> (-4.59%)	⬇️
... and 34 more

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[Wodann]

Nicely done. No comments about the architecture or code; just a couple of requests in terms of spelling, grammar, and documentation.