touchgfx::Widget::getLastChild() method

@fn virtual void Widget::getLastChild(int16_t x, int16_t y, Drawable** last) Function for obtaining the the last child of this widget that intersects with the specified point. Function for obtaining the the last child of this widget that intersects with the specified point. Used in input event handling for obtaining the appropriate drawable that should receive the event. Note that input events must be delegated to the last drawable of the tree (meaning highest z-order / front-most drawable). Only containers can have children, so this implementation simply yields itself as result. The container implementation will filter children that do not intersect with the point or are not visible/enabled, so performing those checks are unnecessary.