C++ Multi-Value support via Tuples & Struct-mapping

[HailToDodongo]

C++ Multivalue

(Needs changes from #305)

The goal is to have easy support for multi-return values in the c++ binding.
Getting the values can either be done via tuples or structure-mapping.

E.g.

// C++17
auto [x,y] = func_a.call_tuple<f32, i32>();
auto [x,y] = func_b.call_tuple<i32, i32>(42.0f);

or

struct Vec3 { f32 x; f32 y; f32 z; };
auto vec = func_a.call_mapped<Vec3>();
auto vec = func_b.call_mapped<Vec3>(42.0f);

TODOs:

• m3 function to map stack to struct
• Unit-tests for internal m3 map function
• C++ multival structure mapping
• C++ multival tuple mapping
• Add Docs

Open Questions:

For unit tests, i assume test/internal/m3_test.c was unused since it wasn't referenced anywhere.
I converted it to a catch2 test which can be run locally and in github actions.
What was the original plan for this file?

[vshymanskyy]

@HailToDodongo sorry for the huge delay. I decided to perform a maintenance release of wasm3, so I hope to review and merge PRs like this finally.