Turn two locator functions into methods

Turn two locator functions into methods

This changes tui_set_locator_fullname and tui_set_locator_info to be
methods on tui_locator_window.  This enables some subsequent
cleannups.

gdb/ChangeLog
2019-08-30  Tom Tromey  <tom@tromey.com>

	* tui/tui-stack.h (struct tui_locator_window) <set_locator_info,
	set_locator_fullname>: New methods.
	* tui/tui-stack.c (tui_locator_window::set_locator_fullname):
	Rename from tui_set_locator_fullname.
	(tui_locator_window::set_locator_info): Rename from
	tui_set_locator_info.  Return bool.
	(tui_update_locator_fullname, tui_show_frame_info): Update.