Space when dragging to shift what's being drawn

For anything that can be dragged with the mouse clicked down, Space should offset it while held down. We have this in a few places (like dragging the next preview segment in the Pen tool), but it should be universal across all dragging actions in every tool.

- Select tool:
- [ ] Transform cage resizing, skewing, and rotating
- [ ] Box and lasso area selection
- Artboard tool:
- [ ] Artboard drawing and resizing
- Gradient tool:
- [ ] Gradient line drawing and endpoint moving
- Path tool:
- [ ] Box and lasso area selection
- Line tool:
- [ ] Line drawing and endpoint moving
- Rectangle/Ellipse/Polygon tools:
- [ ] New shape drawing (and resizing after #1715)
- Text tool:
- [ ] Text area drawing and resizing
- And in the node graph:
- [ ] Box (and lasso after #2532) area selection