Give formal index a proper title.
Use `Pass::formatted_help()` to assign the group, but still return `false` because the help text still comes from `Pass::help()`.
Tidy up some of the affected files' includes to make use of the shared `yosys.h` includes.
Keep techlibs folder hierarchy.
techlibs/* and passes/* groups are now nested under index_techlibs and index_passes respectively, with most (all?) of the passes/* pages getting proper headings, as well as backends/frontends/kernel. `index_passes_techmap` also references `index_techlibs`.
Split command reference toc in twain, one with maxdepth=2 and one with maxdepth=3, since passes and techlibs now have an extra level of nesting.
Move the `cmd_ref` link to the command reference, instead of top of the page.
Remove `index_internal` and `index_other` from the toc, and mark the pages as orphan. Internal commands get a note callout after the command reference toc (although this doesn't work for the pdf build), while other commands are linked in the warning for missing `source_location` (since that *should* be the only time when there are any commands in the "unknown" group).
Update autodoc extension versions, and mark the directives extension as not `parallel_read_safe` (it might be, but I'm not sure about how the xref lookups work if it is parallel so better to be safe).
Commands flagged as internal will display a warning, just like experimental commands.
Drop `passes/tests` group in favour of `internal` group, which is automatically assigned for any command without an assigned group which is flagged as internal.
Changes a bunch of :doc:`/cmd/*` to :cmd:ref:`*` with the intention of changing it later to something that replicates the previous effect of displaying the commands `short_help`.
Removes group parsing from command ref domain, instead relying on a 'groups' object in the cmds.json file.
`docs/source/cmd` is no longer ignored or cleaned.
