This patch adds a new config option: colors{,2}.blur=no|yes. When
enabled, transparent background are also blurred.
Note that this requires the brand new ext-background-effect-v1
protocol, and specifically, that the compositor implements the blur
effect.
Add support for the new xdg-toplevel-tag-v1 Wayland protocol, by
exposing a new config option, `toplevel-tag`, and a corresponding
command option, `--toplevel-tag` (in both `foot` and `footclient`).
This can help the compositor with session management, or custom window
rules.
Closes#2212
