This commit implements a new modifier key (`B`) for the transform
operators.
This new key allows changing the 'Snap Base' of a transform by snapping
it to a defined point in the scene.
Ref #66424
# Implementation Details
- This feature is only available in the 3D View.
- This feature is only available for the transform modes:
- `Move`,
- `Rotate`,
- `Scale`,
- `Vert Slide` and
- `Edge Slide`.
- The `Snap Base Edit` is enabled while we are transforming and we
press the key `B`
- The `Snap Base Edit` is confirmed when we press any of the keys:
`B`, `LMB`, `Enter`
- During um operation, if no snap target is set for an element in the
scene (Vertex, Edge...), the snap targets to geometry Vertex, Edge,
Face, Center of Edge and Perpendicular of Edge are set automatically.
- Constraint or similar modal features are not available during the
`Snap Base Edit` mode.
- Text input is not available during the `Snap Base Edit` mode.
- A prone snap base point is indicated with an small cursor drawing.
Pull Request: https://projects.blender.org/blender/blender/pulls/104443
3010f1233b