Allow FillToEdge to grow when all its edges are blocked. This change points out how useless the return value from client_find_resize_directional() was, so it also removes that. When all edges are blocked, the FillToEdge action will try to grow all four edges agin without blocking any of them on their current edge. This more closely matches the behaviour of the GrowToEdge action.
Clean up the FillToEdge action implementation This extend the client_find_resize_directional() method to support two growing modes, and return a bool for whether it was able to grow/shrink. The client_find_resize_directional() method now takes an enum instead of a bool, with two growing modes. The old mode which always tries to grow, the a new mode that will only grow if the client's edge is not already at a grow stopping point (ie against the edge of another window).