refactor: extract mun_hir_input

[baszalmstra]

Extracts the input part of the hir database into its own seperate crate: mun_hir_input.

The goals is to create a cleaner API separation and at the same time decrease incremental compilation time by splitting crates.

[codecov]

Codecov Report

Attention: Patch coverage is 94.35484% with 7 lines in your changes missing coverage. Please review.

Project coverage is 87.40%. Comparing base (cf1bae3) to head (282fed4).

Files	Patch %	Lines
crates/mun_codegen/src/mock.rs	66.66%	1 Missing ⚠️
crates/mun_codegen/src/module_group.rs	0.00%	1 Missing ⚠️
crates/mun_compiler/src/db.rs	50.00%	1 Missing ⚠️
crates/mun_hir_input/src/module_tree.rs	83.33%	1 Missing ⚠️
crates/mun_hir_input/src/package_set.rs	0.00%	1 Missing ⚠️
crates/mun_language_server/src/analysis.rs	80.00%	1 Missing ⚠️
crates/mun_language_server/src/db.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #571   +/-   ##
=======================================
  Coverage   87.40%   87.40%           
=======================================
  Files         274      276    +2     
  Lines       32543    32531   -12     
=======================================
- Hits        28444    28434   -10     
+ Misses       4099     4097    -2     

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[Wodann]

Two comments but feel free to address them and merge yourself.