The x11-terminal command spawns a potentially long-lived terminal
process. The terminal can is completely independent of the Kakoune
session that created it.
Due to how it's implemented, the spawned terminals will have
environment variables "kak_opt_termcmd" and "kak_quoted_reg_a"
set. This can be surprising, especially since, by convention, the
environment contains no lowercase variables. Let's stop exporting them.
While Wayland offers nothing general to help us support `focus` on all
window managers, WM-specific implementations are generally possible.
Sway is a tiling window manager that mimics i3, and has a reasonably
powerful CLI that can help us achieve this.
In addition to supporting `focus` for Sway, this change paves the way
for additional WM-specific Wayland functionality by adding a detection
step to wayland.kak, in a similar fashion to detection.kak.
