Change tui_check_and_display_highlight_if_needed to be a method

Change tui_check_and_display_highlight_if_needed to be a method

This changes tui_check_and_display_highlight_if_needed to be a method
on tui_win_info.  This makes it clear that the NULL check in that
function is not needed, so it is removed here.

gdb/ChangeLog
2019-08-13  Tom Tromey  <tom@tromey.com>

	* tui/tui-winsource.c (tui_erase_source_content)
	(tui_show_source_content, tui_source_window_base::refresh_all):
	Update.
	* tui/tui-wingeneral.h
	(tui_check_and_display_highlight_if_needed): Don't declare.
	* tui/tui-wingeneral.c
	(tui_win_info::check_and_display_highlight_if_needed): Rename from
	check_and_display_highlight_if_needed.
	* tui/tui-win.c (tui_rehighlight_all)
	(tui_win_info::make_visible_with_new_height): Update.
	* tui/tui-regs.c (tui_data_window::display_registers_from_line)
	(tui_data_window::erase_data_content)
	(tui_data_window::display_all_data): Update.
	* tui/tui-data.h (struct tui_win_info)
	<check_and_display_highlight_if_needed>: Declare.