qxl: support mono cursors with inverted colors

qxl: support mono cursors with inverted colors

Monochrome cursors are still used by Windows guests with the
QXL-WDDM-DOD driver. Such cursor types have one odd feature, inversion
of colors. GDK does not seem to support it, so implement an alternative
solution: fill the inverted pixels and add an outline to make the cursor
more visible. Tested with the text cursor in Notepad and Windows 10.

cursor_set_mono is also used by the vmware GPU, so add a special check
to avoid breaking its 32bpp format (tested with Kubuntu 14.04.4). I was
unable to find a guest which supports the 1bpp format with a vmware GPU.

The old implementation was buggy and removed in v2.10.0-108-g79c5a10cdd
("qxl: drop mono cursor support"), this version improves upon that by
adding bounds validation, clarifying the semantics of the two masks and
adds a workaround for inverted colors support.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1611984
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Message-id: 20180903145447.17142-1-peter@lekensteyn.nl

[ kraxel: minor codestyle fix ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>