Lock / Unlock paint on all sides (supplement to projected brush)

[ThomasFrickHytale]

Detailed description of your suggestion

Once projected brush is solved, we could think about a toggle on/off to allow or not to project on all sides at same time, in the case artists want precise control over their pixel projection

[JannisX11]

This is already implemented and coming in 5.2! JannisX11/blockbench#1898