Nonaquad/nona/miniquad/rawdraw as rendering backends

I just stumbled upon https://github.com/nokola/nonaquad and https://github.com/cntools/rawdraw and they seem they might serve as a good source of inspiration for backends or ever itself be a Nuklear backend.

Review the linked nonaquad and rawdraw projects, then compare them with Nuklear's existing rendering-backend approach. The issue does not name files, tests, a specific backend target, or acceptance criteria, so define those before implementation.

Written by the indexing model from the issue text.