glyphs2ufo: create all parent folders if necessary when writing out UFOs

I.e. a UFO might be saved to `masters/Something.ufo` instead of just `Something.ufo`, so we need to use `mkdir -p` before.

Start at the glyphs2ufo output path handling and trace how a UFO destination such as masters/Something.ufo is written. Ensure missing parent folders are created before writing, then verify that nested output paths succeed without affecting direct UFO output.

Written by the indexing model from the issue text.