There are other events besides `MOUSEMOVE` that's passed in during modal
handling, causes the `tgpi->mvalo` variable to be overwritten without
moving the stroke in the first place, this results in inaccurate offsets
during mouse/pen grabbing in primitive gizmo `IN_MOVE` mode. Now fixed.
Also fixed the operator hint to include the grab functionality.
Pull Request: https://projects.blender.org/blender/blender/pulls/108172
99df159ce0