Initial TUI mouse support

Initial TUI mouse support

Implements an overridable tui_win_info::click method whose arguments
are the mouse coordinates inside the specific window, and the mouse
button clicked.

And if the curses implementation supports 5 buttons, the 4th and 5th
buttons are used for scrolling.

gdb/ChangeLog:

2021-06-04  Hannes Domani  <ssbssa@yahoo.de>

	* ser-mingw.c (console_select_thread): Handle MOUSE_EVENT.
	* tui/tui-data.h (struct tui_win_info): Add click function.
	* tui/tui-io.c (tui_prep_terminal): Enable mouse events.
	(tui_deprep_terminal): Disable mouse events.
	(tui_dispatch_ctrl_char): Handle KEY_MOUSE.
	* tui/tui.c (tui_disable): Disable mouse events.