Add touchscreen support to the tab bar

Add touchscreen support to the tab bar

* lisp/menu-bar.el (popup-menu-normalize-position): Normalize
`touchscreen-begin' events correctly.
* lisp/tab-bar.el (tab-bar-mouse-context-menu): New argument
POSN.  Use it if specified.
(touch-screen-track-tap, tab-bar-handle-timeout)
(tab-bar-touchscreen-begin): New functions.
(tab-bar-map): Bind [tab-bar touchscreen-begin].
* lisp/touch-screen.el (touch-screen-track-drag): Fix doc
string.
* src/dispextern.h: Export `get_tab_bar_item_kbd'.
* src/keyboard.c (coords_in_tab_bar_window): New function.
(make_lispy_event): Adjust touchscreen begin event mouse
position list for tab bar.
* src/xdisp.c (tab_bar_item_info): Allow CLOSE_P to be NULL.
(get_tab_bar_item): Adjust doc string.
(get_tab_bar_item_kbd): New function.