Allow sliding between face buttons, similar to sliding between dpad directions

[jakedowns]

Similar to how you can already (optionally) drag over the d-pad and change directions, in games like mario it's helpful to be able to "rock" between run and jump often times i miss jumps trying to ... jump my thumb between virtual buttons simply dragging out of one, and into the other should solve this (in theory)

Just tracking this here in case anyone else thinks of this and wants to add an issue, we can close it and say dupe of this issue! haha anyway, this is a feature I want, and i'm starting work on it now. I'll publish a pull request soon.