Allow tabs to have consistent given names

Allow tabs to have consistent given names

* lisp/tab-bar.el (tab-bar--tab): Pull automatic name information from
current tab
(tab-bar--current-tab): Pull automatic name information from current
tab, or from new optional template argument
(tab-bar-select-tab): Pass the target tab as a template when setting
it as current tab
(tab-bar-rename-tab, tab-bar-rename-tab-by-name): New functions
* doc/emacs/frames.texi (Tab Bars): Document new tab rename functionality.