RFC: Grid resize (merge request 102)

[Björn Fischer]

Hi folks,

my initial approach for advanced window tiling evolved into something
much different: Grid resize, which allows for much more flexibility
without any additional configuration at the cost of one additional mouse
click.

https://gitlab.xfce.org/xfce/xfwm4/-/merge_requests/102

The patch set is pretty much in a works-for-me state, or even well
within my comfy zone. Sole thing that should be added, probably, is
configurability of the hotkey which currently is hard coded to mouse
button 9 without any modifiers.

Before I further look into configurability I'd like to know if a feature
like grid resize is desirable at all to be included into XFWM. So I
humbly ask for your comments.

Cheers
Björn