Issuing mouse-generated actions to Lua

As part of #893, I'm looking for a way to tell Lua about mouse actions.

Simply sending an array of matching actions as an additional argument of `MousePress`, `MouseMove`, and `MouseRelease` would match how keyboard actions are handled, however, since `MouseMove` and `MouseRelease` are coupled with `MousePress`, is it still worth sending them the action?

Also, would it be worth providing a new set of callins, e.g. `ActionPress`, `ActionUpdate`, `ActionRelease`, to unify action handling?

Start by reading issue #893 and tracing the existing Lua keyboard-action handling. Compare the MousePress, MouseMove, and MouseRelease callins, then evaluate whether mouse-generated actions need new arguments or unified ActionPress, ActionUpdate, and ActionRelease callins. Done means the API direction and handling semantics are agreed and documented for implementation.

Written by the indexing model from the issue text.