Move documentation of this-command buffer display condition entry

Move documentation of this-command buffer display condition entry

* doc/lispref/buffers.texi (Buffer List): Document this-command
buffer display condition entry.
* doc/lispref/windows.texi (Choosing Window): Give an example of
using this-command buffer display condition entry in
display-buffer-alist.
(Buffer Display Action Alists):
* lisp/window.el (display-buffer): Delete documentation of
this-command buffer display condition entry from these locations
because it is not a buffer display action alist entry.
* lisp/subr.el (buffer-match-p): Update cross reference.

(cherry picked from commit d32ab06145a6055f5e39d348bddba72c3f705d75)