input: Allow different surfaces to be interacted in parallel by touch

While on pointers and keyboards the focus patterns follows rather naturally, on touch screens it doesn't so much. This change adapts our touch infrastructure to allow for multiple surfaces to be issued touch events without forcing all interactions into the same one.

Signed-off-by: Victoria Fischer victoria.fischer@mercedes-benz.com

Draft because it needs testing

Tested on a touch-capable laptop, all works fine.