Tweak and Relax: Quick hotkeys

[jlampel]

It would be a huge workflow speedup to be able to quickly use Tweak and Relax while in the other tools like in v3.

Here's what I think the keymap should be:

• Shift LMB Drag: Relax
• Ctrl Shift LMB Drag: Tweak

We have a lot less keys at our disposal in v4 since Blender takes a lot of the combos by default, so we have to be a bit clever. The catch here is that there needs to be a distinction between clicking and click dragging. Holding shift alone would not activate Relax, since we need shift for toggling selection. Instead, the tools should only be activated on drag.

Is that even possible with how Blender handles modals?