rename Jobs renderers to make them explict that use cairo

For the porting to GTK4, it is necessary to have a renderer based on GdkTexture. We are not removing completely the cairo renderers, yet in case we or someone else need it as fallback. We expect to have both EvJobRenderCairo and EvJobRenderTexture, and both EvJobThumbnailCairo and EvJobThumbnailTexture.

Temporarily we are deprecating the cairo renderer, so we do not forget about it. Later on we can decide whether to keep it as it is and remove the guards, or remove the cairo renderer for good.

This MR supersedes !647 (closed) as the original branch diverged a lot, I guess because of the fork of Evince. We do not want to overwrite and mess other branches.