Support for SetCustomCursor in Krom

Krom dont supports change the cursor via kha.input.Mouse.setSystemCursor().

It was nice to have this possibility.

`package arm;

import kha.Image;

class MouseCursorHandler extends iron.Trait {

var current_mouse = kha.input.Mouse.get();
var custom_mouse_image: Image;

public function new() {
super();

notifyOnInit(OnInit);

}

function OnInit() {
iron.data.Data.getImage("DefaultCursor.png", (image: Image) -> {
custom_mouse_image = image;

current_mouse.setSystemCursor(kha.input.Mouse.MouseCursor.Custom(custom_mouse_image));

});
}
}
`
With this code above the mouse cursor is changed when exporting to Web, but in Krom this don't work.

Start by tracing kha.input.Mouse.setSystemCursor() and the Krom path, then compare it with the working Web behavior described in the issue. Done means the provided custom cursor example changes the cursor when exported to Krom as well as on Web.

Written by the indexing model from the issue text.