* lisp/tab-line.el: Add context menu bound to down-mouse-3 like on tab bar.

* lisp/tab-line.el: Add context menu bound to down-mouse-3 like on tab bar.

* lisp/tab-line.el: Bind tab-line down-mouse-3 to tab-line-context-menu.
(tab-line-tab-map): Rebind tab-line-select-tab from mouse-1 to down-mouse-1.
Bind down-mouse-3 to tab-line-tab-context-menu.
(tab-line-add-map): Rebind tab-line-new-tab from mouse-1 to down-mouse-1.
(tab-line-left-map, tab-line-right-map): Rebind mouse-1 to down-mouse-1.
(tab-line-tab-context-menu, tab-line-context-menu): New functions.
(tab-line-hscroll-right, tab-line-hscroll-left)
(tab-line-new-tab, tab-line-select-tab)
(tab-line-switch-to-prev-tab, tab-line-switch-to-next-tab)
(tab-line-close-tab): Rename event args to 'event'.