Resurrect mouse-highlight of close buttons on tab-bar

Resurrect mouse-highlight of close buttons on tab-bar

* src/w32term.c (w32_draw_image_relief): Support tab-bar drawing
with relief as xterm.c does.

* src/xdisp.c (handle_tab_bar_click): Access the mouse-highlight
info.  Call show_mouse_face to show the button in the pressed or
the released state, according to value of DOWN_P.
(note_tab_bar_highlight): Function added back.
(note_mouse_highlight): Call note_tab_bar_highlight when the mouse
pointer is in the tab-bar window.
(show_mouse_face): Return immediately if mouse_face_window is not
set up in HLINFO.  This avoids rare assertion violations.