Blender Git Loki

Fix straightline gesture snapping not working for modal tools

This was implemented in {rB14d56b4217f8} but was never working for
tools/operators other than the sculpt line mask tool.

To be precise, the preview actually snapped but the operations (e.g.
mesh bisect, vertex weight gradient) still happened "unsnapped" in
modal. For the sculpt line mask tool this wasnt a problem, because it
only draws a preview while modal, the actual mask was only applied
later.

This solves part one of T91320 (snapping), sculpting also introduced
flipping in {rB7ff6bfd1e0af} which does not make much sense for all
tools, but in bisect this could actually be supported, will add that in
a separate Diff.

ref T91320

Maniphest Tasks: T91320

Differential Revision: https://developer.blender.org/D12470