Also see #103343.
Couldn't move two files yet:
* `softbody.c`: The corresponding regression test fails. It seems like the
conversion to C++ changes floating point accuracy, but it's not clear where that happens exactly.
* `writeffmpeg.c`: Is a bit more complex to convert because of the static array in `av_err2str`.
Pull Request: https://projects.blender.org/blender/blender/pulls/110182
