Upgrade X11 and desktop chapters in the Handbook

Changes in X11:

• Rewrite the chapter to reflect the current status of the graphics in FreeBSD
• Remove old references to *really* old Intel drivers, old configurations, compiz, etc.
• Move desktop environments instructions to Desktop Environments chapter right now desktop environments like KDE Plasma or GNOME are not tied to X11 since support also Wayland

Changes in Desktop:

• Upgrade instructions to install KDE Plasma, GNOME and XFCE
• Add instructions to install MATE, Cinnamon and LXQT
• Upgrade Firefox and Chromium sections
• Add Iridium, Falkon, Epiphany, qutebrowser and Dillo
• Add a new section with development tools: VS Code, Qt Creator, Vim, etc.
• Upgrade Desktop office productivity section
• Upgrade Document Viewers section
• Upgrade Finance section

Reviewed by: arrowd@, jrm@, karels@, manu@, fernape@
Differential Revision: https://reviews.freebsd.org/D38143