Wang brush mode for both Edges and Corners

[therahedwig]

Also noted in the Wang Tile task feedback.

Right now, we can only paint with edges or corners with the wang brush. I would like to have a mode that tries to do both edges and corners.

In particular, Blob-style wang tilesets are named that way because we can consider the center of the tile to always contain a "blob" of "color". I would like to be able to paint with the wang tile brush in a manner that considers the center of the tile as a blob of color and chooses the right tiles from that.