Add tests for Projection

[Flarkk]

This PR adds nearly full test coverage for struct Projection.

The following few methods are not covered yet and left to further PR(s) :

• set_for_hmd() and create_perspective_hmd()
• set_perspective() with eye input
• set_orthogonal() with aspect input and create_orthogonal_aspect()
• set_frustum() with aspect input and create_frustum_aspect()
• get_pixels_per_meter()
• get_lod_multiplier()
• and a few operators (==, !=, Transform3D)

[Flarkk]

Sorry for these repeated force push. The workflow stopped on a weird error with asan. I ended up removing the DOCTEST_STRINGIFY_VARIANT I had added for Vector4, Vector4i and Projection in test_macros.h as I suspect it was related to the stringification logic. I couldn't investigate further for now so as a quick fix I simply removed them. I hope it's ok now.

[Flarkk]

Last force push I hope... Everything builds and runs fine in my environment

[Flarkk]

Allright, ready for review !

[Flarkk]

Rebased on top of #95303

[Calinou]

Looks good to me.

[akien-mga]

Thanks!