devel-docs: Introspected Python libgimp and libgimpui docs generation.
Based on the proposed process proposed by Akkana Peck. Thanks Akk! For now, it's only in the meson build, which is fairly terrible to use as soon as we do custom build rules. Here are the list of issues: - meson does not allow building in subdir (issue 2320 on meson tracker). Sure I could make several subdirs with meson in them. But here the future goal would be to be able to generate docs for other introspected languages, and maybe also other output formats (epub or whatnot). For this, since these are basically the same commands which are used, the best practice would be to have loops generating one target per language/format combination, reusing code rather than ugly copy-pasting in subdirectories' meson files). - custom_target() requires the output parameter to be the complete list of generated files. But we have more than a thousand of them. It's not practical. Maybe we could try to find a way to generate the list from the contents of the .def files which are already exhaustive and exact. - Install also requires the output list to be complete. - I temporarily have these docs not generated by default (because the gtk-doc option is already crazy slow as it is, making meson near unusable for development if it's enabled). If you want to generate the docs, the commands are as following (yeah I don't understand what the target names are for since meson does not actually create targets with these names, so we have to use fake output names instead): > ninja devel-docs/g-ir-docs/Gimp-python-html > ninja devel-docs/g-ir-docs/GimpUi-python-html