Introduce set_new_height method

Introduce set_new_height method

This introduces tui_win_info::set_new_height and implements it in the
subclasses as appropriate.  This removes another switch on the window
type.

gdb/ChangeLog
2019-06-25  Tom Tromey  <tom@tromey.com>

	* tui/tui-win.c (tui_source_window_base::set_new_height)
	(tui_data_window::set_new_height): New methods.
	(make_invisible_and_set_new_height): Call set_new_height method.
	* tui/tui-data.h (struct tui_win_info)
	(struct tui_source_window_base, struct tui_data_window)
	<set_new_height>: New method.