LUA: Add possibilty to hide the mouse pointer

[kaputtnik]

In a scenario, when the map is moved, the mouse pointer 'suddenly' moves over the screen as long the mouse isn't moved by hand. This looks annoying.

Suggestion(s):
1. Hide the mouse pointer as long scroll_to_field() or similar functions are executed
2. Make sure the pointer is always at the same position as scroll_to_field() or similar functions are executed
3. Make an extra function hide_mouse(), so it could be used when needed

There are already some functions related to the position of the mouse pointer, maybe one of them can be reused, see: https://wl.widelands.org/docs/wl/autogen_auxiliary_ui/

[GunChleoc (gunchleoc)]

Migrated to https://github.com/widelands/widelands/issues/2072