Share the window name completion code from the focus command with the
winheight command, providing window name completion for the winheight
command.
gdb/ChangeLog:
* tui/tui-win.c (window_name_completer): New function.
(focus_completer): Call window_name_completer. All old content
moved into window_name_completer.
(winheight_completer): New function.
(_initialize_tui_win): Rename variable. Add completer to
winheight command. Update doc string on winheight.
97605e61a1