Move locator code to tui-stack.c

Move locator code to tui-stack.c

The locator is mostly implemented in tui-stack.c.  This moves the
remaining bits to tui-stack.c and tui-stack.h, as appropriate.

gdb/ChangeLog
2019-08-15  Tom Tromey  <tom@tromey.com>

	* tui/tui-wingeneral.c: Include tui-stack.h.
	* tui/tui-stack.h (MAX_LOCATOR_ELEMENT_LEN)
	(struct tui_locator_window): Move from tui-data.h.
	* tui/tui-stack.c (_locator, tui_locator_win_info_ptr)
	(tui_initialize_static_data): Move from tui-data.c.
	* tui/tui-data.h (MAX_LOCATOR_ELEMENT_LEN)
	(struct tui_locator_window): Move to tui-stack.c.
	* tui/tui-data.c (_locator, tui_locator_win_info_ptr)
	(tui_initialize_static_data): Move to tui-stack.c.