Add Mesh Importer modals for grabbing (G) rotating (R) and scaling (S) the scene

[adamkewley]

Estimate: 4-8d

This is a fairly big feature that tries to mimic how Blender works.

The idea is that users can click G, R, or S in a 3D scene to temporarily enter a "mode" in that screen that performs the specific action. The user can also press X, Y, or Z while in that mode to perform a transform in that axis.

E.g. this would enable a user:

• Clicking something to select it
• Pressing G to enter "grab" mode
• Pressing X to enter "grab X" mode
• Typing a number to move the element along X
• Pressing enter to commit to the change, or ESC to back out of the mode

The benefit of this UX feature is that it removes the user from having to use the right-click menu or on-screen gizmos, which are harder to click.