Replace almost "render" to "paint" words in gfx crate.
Replace almost "render" to "paint" in compositing crate.

This doesn't touch some "render" words which are used as general means.
Replace almost "render" to "paint" in layout crate.

This doesn't touch some "render" words which are used as general means.
Replace render to paint in util/opts.rs. Some general words are not replaced.