Sculpt: Add customizable increment for line tool snapping
This PR exposes the snap increments introduced in #118760 to the base
`WM_gesture_straightline` operators and exposes the increment menu to
allow users to change this value in both Sculpt and Weight Paint mode.
## Details
The full list of operators this affects:
* IMAGE_OT_sample_line
* PAINT_OT_weight_gradient
* MESH_OT_bisect
* PAINT_OT_mask_line_gesture
* SCULPT_OT_trim_line_gesture
* SCULPT_OT_project_line_gesture
* PAINT_OT_hide_show_line_gesture
## Compatibility
Previously, the hardcoded value for this snap increment was 15 degrees,
by using the toolsetting value, this changes the default to 5 degrees.
Pull Request: https://projects.blender.org/blender/blender/pulls/121547
1cf0d7ca6a