We've long used a switch statement on the grab operation to determine
where events should go. The issue with MetaGrabOp is that it's a mixture
of a few different things, including event routing, state management,
and the behavior to choose during operations.
This leads to poorly defined event routing and hard-to-follow logic,
since it's sometimes unclear what should point where, and our utility
methods for determining grab operations apart can be poorly named.
To fix this, establish the concept of a "event route", which describes
where events should be routed to.
Popups could not set the cursor image, because the cursor tracker would
ignore window cursors if we had a popup active. The correct condition to
check for is already in should_block_wayland. Rename this to the more
sensible name windows_are_interactable, and use it in the cursor tracker.
We expect that meta_screen_set_cursor while grabbed will properly
set the cursor on the root window. Make sure this works by simply
always using the root cursor when we have an active grab.
Now that we have a global MetaScreen, we can simply have a global
MetaCursorTracker as well. Keep the get_for_screen() API around for
compatibility, though.
Right now this just has all of the files in one directory. We'll
be introducing more structure to this in the future, and build
a proper backend system.
