This patch adds support for observing multiple slices of the desktop background.
This is used for the tray so that it doesn't have to rely on the bar's rect to
get the desktop background. In particular, it now handles the case where the
tray is not contained fully within the bar's outer rect (for example, when using tray-offset-{x,y})
Co-Authored-By: bennofs <benno.fuenfstueck@gmail.com>
7256366112