Add moving unconstrained bit to moving grab-mode

[jmmaranan]

Fixes #201 - added new grab op bit to recognize moving grab mode.

[mooey5775]

One very minor comment - I think moving windows now with Alt + F7 and arrow keys emits KEYBOARD_MOVING | unconstrained bit, which isn't currently matched by the modified if statement. A slight complication is that this combination of bits isn't directly exposed by the GrabOp enum - it might require some bit magic to work if you'd like to support it.

See https://gitlab.gnome.org/GNOME/mutter/-/commit/12773cf8e2954082f346dee300af624b25baf23c for relevant code

[jmmaranan]

Thank you @mooey5775, Forge does not use Alt + F7 or default move-window builtin to GNOME because I couldn't find the solution for it. So I implemented window swapping/moving with shortcuts instead in Forge. But I certainly can try to add the unconstrained bit to complete the builtin support for GNOME. Thank you for the tip!

[jmmaranan]

Tested in Fedora 38 Silverblue. And works as expected