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