* lisp/tab-bar.el: In tab switching allow absolute and relative args.

* lisp/tab-bar.el: In tab switching allow absolute and relative args.

* lisp/tab-bar.el (tab-bar-tab-hints): New defcustom.
(tab-bar-make-keymap-1): Use tab-bar-tab-hints.
(tab-bar--tab, tab-bar--current-tab, tab-bar--current-tab-index)
(tab-bar--tab-index, tab-bar--tab-index-by-name): New internal functions.
(tab-bar-select-tab): Use arg as absolute position of tab to select.
(tab-bar-switch-to-next-tab, tab-bar-switch-to-prev-tab): Use arg
as offset relative to the current tab.
(tab-bar-switch-to-tab): New command.
(tab-bar-new-tab): Simplify by using cl-pushnew.
(tab-bar-close-current-tab): Remove (the current tab is closed
by nil arg of tab-bar-close-tab).
(tab-bar-close-tab): Use arg as absolute position of tab to close.
(tab-bar-close-tab-by-name): New command.