Catch2 v3+ Support

[ax3l]

Catch3 introduces a few breaking changes and adds a neat no-header-only build by default.

Also, its CMake package is not marked as compatible with version 2 find_package, so we need to add manual support for it.
Conda-Forge for instance already ships Catch2 v3.

[ax3l]

#1823 seems to need a bit more work, let's do it in 0.18.0