feat(codegen): add AsValue macro support for enums

[Wodann]

Closes #275

[codecov]

Codecov Report

Merging #286 into master will decrease coverage by 0.05%.
The diff coverage is 69.23%.

@@            Coverage Diff             @@
##           master     #286      +/-   ##
==========================================
- Coverage   79.39%   79.34%   -0.06%     
==========================================
  Files         220      220              
  Lines       13004    13069      +65     
==========================================
+ Hits        10324    10369      +45     
- Misses       2680     2700      +20     

Impacted Files	Coverage Δ
crates/mun_codegen/src/ir/types.rs	37.50% <0.00%> (-37.50%)	⬇️
crates/mun_codegen/src/value/array_value.rs	77.77% <0.00%> (-3.62%)	⬇️
crates/mun_codegen/src/value/string.rs	21.42% <ø> (ø)
crates/mun_codegen/src/value/pointer_value.rs	64.28% <25.00%> (-15.72%)	⬇️
crates/mun_codegen/src/value/float_value.rs	30.00% <75.00%> (+30.00%)	⬆️
crates/mun_codegen/src/value/mod.rs	60.86% <80.00%> (+7.80%)	⬆️
crates/mun_codegen/src/mock.rs	82.22% <83.33%> (+0.17%)	⬆️
crates/mun_codegen/src/value/int_value.rs	66.66% <100.00%> (+20.23%)	⬆️

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[baszalmstra]

First little batch, Im gonna wait until this is rebased to get a better overview of the changes. :)

[Wodann]

I need to add trivial tests for as_bytes_and_ptrs as the test coverage is too low.

[baszalmstra]

This is really nice and also provides a valuable start to add enums to Mun itself!

In general I think it would be good to split the generation of enums and structs in seperate functions, maybe add some more helper functions. This procedural macro function is now almost 700 lines long which IMO is way to long for a single function.

Also, again, some comments explaining what is going on would be nice. Maybe you could even add a little explaination in the docs what the problem is and how it is solved? (Either in the book or as doc comments)