Mouse wheel scrolling on the tab bar

Mouse wheel scrolling on the tab bar

* lisp/tab-bar.el (tab-bar-map): Bind mouse-4/wheel-up/wheel-left
to tab-previous and mouse-5/wheel-down/wheel-right to tab-next.
Bind S-mouse-4/wheel-up/wheel-left to tab-bar-move-tab-backward
and S-mouse-5/wheel-down/wheel-right to tab-bar-move-tab.
(tab-bar-move-tab-backward): New command.
(tab-bar-move-repeat-map): Use tab-bar-move-tab-backward
instead of lambda.

* src/xterm.c (handle_one_xevent): Remove restriction
to allow clicking mouse-4 and mouse-5.