The mouse binding logic is inspired/copied from the
keyboard binding logic; we store a sorted list of the
currently pressed buttons, and trigger a binding when
the currently pressed (or just recently pressed, in
the case of a release binding) buttons, as well as
modifiers/container region, match those of a given
binding.
As the code to execute a binding is not very keyboard
specific, keyboard_execute_command is renamed to
seat_execute_command and moved to where the other
binding handling functions are. The call to
transaction_commit_dirty has been lifted out.