Until now, Seat.setFocusRaw sent all pressed keys to the client,
including ones that should be eaten. (Try e.g. changing focus to a
nested wlroots compositor with a terminal open to easily see it.)
However, only filtering out the eaten keys is not enough; they were
eaten only once all mappings had been executed. Therefore, the original
function had to be split into one looking up mappings and another
executing them.
Until now, only the event (press/release) for which a mapping was
present got eaten, and the other was passed to the client. From this
commit, a press mapping eats both events and a release mapping eats
nothing (and a press+release combo eats both).
This fixes behavior of some clients that do not make a difference
between press and release (e.g. Firefox with a fullscreen video
exiting fullscreen even on an Esc release event).