This follows up 8dc429165c9a354ffb18703598ea923d7f5e9e9a, which forgot to
stage the libxkbcommon dependency. While at it, reindent, and make SCDOC a
native input.
* gnu/packages/image.scm (slurp)[inputs]: Add LIBXKBCOMMON. Move SCDOC ...
[inputs]: ... here.