Instead of creating a GdkX11Cursor, create GdkCursors. Cache the XCursor
in a hash table instead.
Also, make use of the new fallback mechanism for fallback code: Make
sure to provide cursors for the names that are guaranteed to exist, but
do not do bad attempts at displaying texture surfaces.
Black/White/transparent is not a replacement for those.
Interpret NULL as "root window" here - we only have one
screen nowadays, so there is no choice involved, and this
will let us avoid dealing with the root window in the
fontend code.
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.
If you set GDK_SCALE=2 in the environment then all windows will be
scaled by 2. Its not an ideal solution as it doesn't handle
multi-monitors at different scales, and only affects gtk apps.
But it is a good starting points and will help a lot on HiDPI
laptops.
