* lisp/tab-bar.el: Use autoloaded seq-position.

* lisp/tab-bar.el: Use autoloaded seq-position.

* lisp/tab-bar.el (tab-bar--current-tab-index)
(tab-bar--tab-index, tab-bar--tab-index-by-name):
Use seq-position.

(tab-bar-select-tab, tab-bar-new-tab, tab-bar-close-tab)
(tab-bar-close-other-tabs, tab-bar-rename-tab)
(tab-bar-list-execute): Call force-mode-line-update
unconditionally independent from tab-bar-mode.

(tab-bar-rename-tab, tab-bar-rename-tab-by-name):
Use read-from-minibuffer instead of read-string
to be able to enter empty string.