rework TTY_PERM_INVENT; update window port interface

Change the inner workings of the experimental TTY_PERM_INVENT.

Switch to delivering the content to tty for the experimental perm_invent
via the existing window port interface (start_menu(), add_menu(), end_menu).

This also adds a new window port interface call ctrl_nhwindow() for
delivering information to the window port, and/or obtaining specific
information from the window port. The information and requests can
be extended as required. To be documented later once the changes settle
down.

Due to the intrusive nature of these changes and the possibility of
some bugs in the new code, I'm going to leave TTY_PERM_INVENT commented
out in the repository for a day or two.  Anyone wishing to test it out
can do so by uncommenting TTY_PERM_INVENT in config.h.

include/decl.h

@@ -972,8 +972,10 @@ struct instance_globals {
        persistent one doesn't get shrunk during filtering for item selection
        then regrown to full inventory, possibly being resized in the process */
     winid cached_pickinv_win;
-    winid perm_invent_win;
     int core_invent_state;
+    int in_sync_perminvent;
+    int perm_invent_toggling_direction;
+    long glyph_reset_timestamp;
 
     /* query objlist callback: return TRUE if obj type matches "this_type" */
     int this_type;