Use images for new/close buttons in tab-bar and tab-line.

Use images for new/close buttons in tab-bar and tab-line.

* etc/images/tabs/new.xpm:
* etc/images/tabs/close.xpm:
New files.

* lisp/tab-bar.el (tab-bar-separator): New face.
(tab-bar-separator, tab-bar-button-new, tab-bar-button-close):
Use display property with images in default values.

* lisp/tab-line.el (tab-line-button-new, tab-line-button-close):
Use display property with images in default values.

* src/xdisp.c (tab_bar_item_info): Add new arg close_p and set it
to the value of property `close' at charpos.
(get_tab_bar_item): Add new arg close_p.
(handle_tab_bar_click): Add ctrl_modifier when close_p is non-nil.
(Fdump_tab_bar_row): Fix crash for non-X builds.