Revamping gnome-help style

Hi all,

I've been working on some style revamps for gnome-help for GNOME 40. It
started with just getting rid of desc links, but it grew into a whole
thing. Please take a look at this WIP MR:

https://gitlab.gnome.org/GNOME/gnome-user-docs/-/merge_requests/102

Current things I'm looking at:

* Stop putting links in desc elements, because they make everything
just way too dense and hard to navigate.

* Along the same lines, stop using the "toronto" grid style that was
largely designed around links in desc elements.

* Put shorter titles in link trails.

* Use curly quotes/apostrophes instead of straight quotes/apostrophes.

* Stop putting icons in title elements, because they don't scale well
and cause various problems. I have thoughts on putting a splash image
on the front page, but haven't done much work along those lines yet.

* Use a new experimental icon tile presentation for the front page of
gnome-help (and possibly other prominent guide pages). I've named the
style in yelp-xsl "experimental-gnome-tiles" to really drive home that
this is experimental and I don't want other docs to use it. I want to
be able to iterate on it quickly without worrying about how many docs
I'm affecting.

There are some screenshots in the MR.

--
Shaun