feat: Adds data structures

[Wodann]

This PR adds struct declarations.

The following code should work properly (As the struct definition is still WIP, the example code might change.):

struct A;
struct B {}
struct C {
    pub a: float,
    pub b: int,
}
struct D(float, int)

fn foo(a: C) -> C {
    c.a = 2.0;
    c
}

• Implement parsing of struct declarations.
• Implement type inferencing and diagnostics for struct declarations
• Implement code generation for struct declarations
• Implement parsing of struct literals
• Implement type inferencing and diagnostics for struct literals
• Implement code generation for struct literals
• Implement ABI type for struct declarations

[codecov]

Codecov Report

Merging #64 into master will increase coverage by 2.61%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
+ Coverage   72.14%   74.75%   +2.61%     
==========================================
  Files         109      117       +8     
  Lines        7283     8868    +1585     
==========================================
+ Hits         5254     6629    +1375     
- Misses       2029     2239     +210

Impacted Files	Coverage Δ
crates/mun_codegen/src/ir.rs	80% <ø> (+10%)	⬆️
crates/mun_syntax/src/tests/lexer.rs	100% <ø> (ø)	⬆️
crates/mun_syntax/src/parsing/grammar/types.rs	95.23% <ø> (ø)	⬆️
crates/mun_syntax/src/lib.rs	89.09% <ø> (+1.81%)	⬆️
crates/mun_syntax/src/ast.rs	81.25% <ø> (ø)	⬆️
crates/mun_codegen/src/ir/function.rs	92.3% <ø> (ø)	⬆️
crates/mun_hir/src/db.rs	100% <100%> (ø)	⬆️
...tes/mun_syntax/src/parsing/grammar/declarations.rs	88.52% <100%> (+16.52%)	⬆️
crates/mun_codegen/src/db.rs	100% <100%> (ø)	⬆️
crates/mun_runtime/src/test.rs	96.81% <100%> (+0.46%)	⬆️
... and 79 more

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[baszalmstra]

Implement POD structs

[Wodann]

Add language support for POD structs