ENH: Improve report usability

[larsoner]

I'm using mne.Report for some data analyses and hit some limitations. This PR proposes a few different things, quoting the changelog entry:

- :meth:`mne.Report.add_projs` can now plot with :func:`mne.viz.plot_projs_joint` rather than :func:`mne.viz.plot_projs_topomap`
- :class:`mne.Report` now has attributes ``img_max_width`` and ``img_max_res`` that can be used to control image scaling.
- :class:`mne.Report` now has an attribute ``collapse`` that allows collapsing sections and/or subsections by default.
- :func:`mne.viz.plot_head_positions` now has a ``totals=True`` option to show the total distance and angle of the head.

The first is a fairly straightforward improvement to add_projs to make use of plot_projs_joint instead of plain plot_projs_topomap when you want to do so.

Next is adding a few attributes to mne.Report to control behavior of 1) image scaling, and 2) section collapsing. I never liked that I couldn't get full-res images using the default functions like add_raw or add_projs, now you can set report.img_max_width = None to stop it from shrinking those plots, e.g. on main (you'll need to open separately to see the downscaling quality issue):

On this PR you get full res (up to the browser max-width 100% limitation):

And for section collapsing, I added support for collapsing sections and/or subsections by setting report.collapse = ["section", "subsection"]. I think this is a good enough start, but I think it's also future compatible with potentially also supporting regex-matching to HTML subsection titles for example.

Finally, it adds an option to plot_head_positions to summarize the distance and rotation in terms of the vector magnitude and angle. The distance is nice, but the big gain I think is the angle as it's a lot more human-readable than the quats themselves, e.g.:

Draft mode since I need to add tests for all of this stuff and modify some examples but I figured I'd open this to get the ball rolling. I could split these off if it would help review, but happy to keep them together if review will be doable with them all in one place. (Or at least the report stuff together in one PR, and the head pos stuff in another.)

[larsoner]

Okay tests added, this one should be good to go!

[drammock]

looks good! My suggestions are super minor, feel free to apply them in with ci skip and manually merge. Thanks @larsoner!

[drammock]

huh, was position previously in meters but labeled as millimeters? oops.

[larsoner]

They were in mm before but it was done by modifying destination inplace earlier. So no bugfix just a change in where the multiplication happens!