Combine/union mode for lasso fill tool

[lan700ng]

an idea adding some option for Lasso Fill tool

• Eraser mode
• Combine/Union, Exclusion toggle ( currently default operation on Lasso fill when you draw lasso freely is Exclusion)

[askmeaboutlo0m]

Erase mode already exists, just change the mode from Normal to Erase.

Union mode would be a valid feature, but it's not supported by the underlying paint system. So it's unlikely to be implemented anytime soon, since it's a lot of work to rewrite the entire polygon paint system for a pretty obscure feature.