CI: Refactor config, add Android NDK testing
This does a few things:
- Updates CI to use the newer https://gitlab.freedesktop.org/freedesktop/ci-templates CI templates (which simplifies things)
- Adds a pair of Android NDK builds to the CI
- Adds some configs to the CI that are commonly broken (no OpenGL, no OpenCV, no SDL2)
- Fixes the build issues that those additional CI jobs found.