Rename make_ functions to _create
Implement set_cursor and set_feedback

This adds the management code to manage tablet tools lifetimes from
libinput.
It follows the suggestion made in the tablet-unstable-v2.xml to destroy
tablet_tools once all tablets that it got into contact with were removed
from the system. This is implemented via a refcount.

If a tool is *not* unique, it will be destroyed on proximity out. This
is libinput specific and mentioned in libinput docs that tools will not
be found again, so we shouldn't keep a reference to them.
Also they can't be on other tablets as well, because they cannot be
tracked.

The naming in this commit is a bit off (to not break things).
The wlr names stay the same, tablet_tool is the libinput_device with
capaiblity LIBINPUT_DEVICE_CAP_TABLET_TOOL which is more akin to
"tablet" in the tablet-unstable-v2 protocol.
The struct that corresponds to the tablet_tool in tablet-unstable-v2 is
called tablet_tool_tool, a rename should be done at some point in the
future.

And extend tablet example with tilt and ring support

We now use doubles until the last minute, which makes it so we can move
the pointer more precisely. This also includes a fix for tablet tools,
which move absolutely and sometimes do not update the X or Y axis.

- 'libinput' (backend's) to libinput_context
- 'device' (libinput_device) to libinput_dev
- 'dev' (wlr_device) to wlr_dev
- 'devices' lists tangling of libinput devices to wlr_devices
- 'devices' list of wlr_devices in backend state to wlr_device_lists