kiosk-shell: Add a border fill to non-fullscreen views

This series address an issue pointed out in !702 (comment 1109979) where we where not installing a border fill for surfaces not covering the entire output.

This series does a bit of moving common code, in the first two patches, which I've extract from an older series, specifically, from !569 (merged). If this gets merged before that, I'll remove them from that series.

^ No longer applies in latest version, it has been migrated to !721 (merged)

Additional we correct #553 (closed) and we make the border fill respect the background surface color. With this series we add surface labels which we where also missing.

^ Same as above, no longer applies, being added in !721 (merged)