* lisp/tab-bar.el: Use customizable button icons (bug#51309, bug#51648)

* lisp/tab-bar.el: Use customizable button icons (bug#51309, bug#51648)

* lisp/tab-bar.el (tab-bar--load-buttons): Use 'define-icon' to
define icons for tab-bar-new, tab-bar-close, tab-bar-menu-bar.
Also set tab-bar-new-button, tab-bar-close-button, tab-bar-menu-bar-button
to the specified icon-string.
(tab-bar-history-mode): Use 'define-icon' to
define icons for tab-bar-back, tab-bar-forward.
Also set tab-bar-back-button, tab-bar-forward-button
to the specified icon-string.

* lisp/emacs-lisp/icons.el (icons--create)<image>: Allow to easy
add new image props by using 'apply' on them.  Add :margin.