handbook/x11: refactor

General:
+ Add many search keywords to tags
+ Add detail to subsections, and an abstract
+ Add drm and kms to glossary

Graphics:
+ drivers logically come first, and explain why we have to install them
+ intel graphics is not always integrated and not always cards
+ add graphics to keywords
+ refactor for flow
+ add markup for linking

Xorg:
+ add an overview subchapter
+ disambiguate Xorg server/X Window System
+ xorg-ins should directly precede xorg-cfg
+ try to tersely explain why at more points
+ autoconfiguration should not be a warning in a previous chapter,

it needs to be part of the introduction to configuration

+ explain libinput, and atomic configuration via xinput and setxkbmap
+ explain why we have xf86-input drivers, there are good use cases

Fonts:
+ sort and sync fonts intro
+ truetype fonts are what most users are looking for, for screens.
+ postscript fonts are specialized for typography, for printing.
+ therefore, move truetype first, and explain the difference.
+ add fonts to keywords

Outstanding:
+ hybrid graphics
+ the fonts section really needs more love, the X freetype module does

not actually exist for many years.

+ xorg configuration => see desktop environments
+ ...the whole thing could still be a little clearer
+ mention fwget
+ consider moving driver installation to basics

Discussed with: bcr, carlavilla, vishwin, Jim Brown
Differential Revision: https://reviews.freebsd.org/D46248