Linking to optiongroups doesn't add *that* much, and is kind of a pain; meanwhile having the optiongroups adds an extra level of indentation.
Instead of options needing to be in an option group, they instead go in either the root node or nested in a usage node. Putting them in a usage node allows for more-or-less the previous behaviour but without making it the default.
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).
Calling :cmd:title:`<cmd>` will generate a cross reference to `<cmd>`, but unlike :cmd:ref: which displays a literal block and puts the title (short_help) in the hovertext (the title field of an a-ref), :cmd:title: will display "<cmd> - <short_help>" as plain text.
Thus replacing the previous use case of referring to :doc:`cmd/<cmd>`.
Also refactor util py scripts to have more descriptive names.
