refactor: detect cyclic type aliases and leaked privacy in validator

[Wodann]

Resolves #339

Should be merged after #527

[codecov]

Codecov Report

Merging #528 (e2effb5) into main (d533fce) will decrease coverage by 0.02%.
The diff coverage is 80.67%.

@@            Coverage Diff             @@
##             main     #528      +/-   ##
==========================================
- Coverage   84.35%   84.34%   -0.02%     
==========================================
  Files         275      275              
  Lines       31102    31184      +82     
==========================================
+ Hits        26236    26302      +66     
- Misses       4866     4882      +16     

Impacted Files	Coverage Δ
crates/mun_codegen_macros/src/lib.rs	0.15% <0.00%> (-0.01%)	⬇️
crates/mun_hir/src/ty.rs	76.56% <ø> (+2.09%)	⬆️
crates/mun_hir/src/ty/infer/type_variable.rs	79.55% <55.55%> (-1.95%)	⬇️
crates/mun_hir/src/diagnostics.rs	65.01% <60.00%> (-0.13%)	⬇️
crates/mun_hir/src/expr/validator.rs	98.73% <98.27%> (-0.27%)	⬇️
crates/mun_hir/src/code_model/function.rs	93.75% <100.00%> (-0.06%)	⬇️
crates/mun_hir/src/code_model/struct.rs	97.16% <100.00%> (-0.02%)	⬇️
crates/mun_hir/src/code_model/type_alias.rs	93.10% <100.00%> (+14.97%)	⬆️
crates/mun_hir/src/db.rs	100.00% <100.00%> (ø)
crates/mun_hir/src/expr/validator/tests.rs	100.00% <100.00%> (ø)
... and 5 more

... and 3 files with indirect coverage changes