feat(runtime_capi): add functions for interoperability

[Wodann]

Depends on #87.

[codecov]

Codecov Report

Merging #88 into master will increase coverage by 1.36%.
The diff coverage is 99.06%.

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
+ Coverage   75.32%   76.68%   +1.36%     
==========================================
  Files         121      122       +1     
  Lines        9613     9827     +214     
==========================================
+ Hits         7241     7536     +295     
+ Misses       2372     2291      -81

Impacted Files	Coverage Δ
crates/mun_runtime_capi/src/lib.rs	95.89% <95.45%> (+95.89%)	⬆️
crates/mun_runtime_capi/src/tests.rs	99.47% <99.47%> (ø)
crates/mun_abi/src/autogen_impl.rs	94.77% <0%> (+0.2%)	⬆️
crates/mun_codegen/src/code_gen/symbols.rs	97.2% <0%> (+0.69%)	⬆️
crates/mun_runtime_capi/src/error.rs	47.36% <0%> (+47.36%)	⬆️
crates/mun_runtime_capi/src/hub.rs	78.57% <0%> (+78.57%)	⬆️

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[Wodann]

Add marshalling of structs to C++