New buffer display action function 'display-buffer-in-direction'

New buffer display action function 'display-buffer-in-direction'

* lisp/window.el (windows-sharing-edge)
(window--try-to-split-window-in-direction)
(display-buffer-in-direction): New functions.
* doc/lispref/windows.texi (Buffer Display Action Functions):
Describe new action function 'display-buffer-in-direction'.
(Buffer Display Action Alists): Describe new entry 'direction'.
Amend description of 'window' entry.
* etc/NEWS: Mention 'display-buffer-in-direction' and 'direction'
and 'window' action alist entries.