There's places where we still need to deal with floating devices, which are
unseen by seats. Ignore deprecations and keep using GdkDeviceManager until
we can forget about floating devices.
In various places, the broadway backend was just using
the default display and assumed that it is the broadway
display. That may not be the case in a multi-backend world,
so instead iterate over all displays and use the first
broadway display - still not perfect, but enough to survive
for now.
We've long had double precision mouse coordinates on wayland (e.g.
when rotating a window) but with the new scaling we even have it on
X (and, its also in Xinput2), so convert all the internal mouse/device
position getters to use doubles and add new accessors for the
public APIs that take doubles instead of ints.
This (shouldn't) change any behaviour, but it moves the
webserver parts to a separate file, making the broadway display file
smaller and preparing for later separating out the server to its own
process.
Event times come from the browser and may change weirdly when we reconnect
with another browser, so we normalize these to be strictly increasing
and with a 5 second gap for each reconnect.
Since we're really only initializing grabs (except for implicit
grabs at least) from the client side we might as well do all the grab
time checks on the client side to avoid unnecassary roundtrips.
