Fix Tooltip inside Scrollable

[tarkah]

Tooltip inside Scrollable is currently broken since the viewport passed to the Tooltip is modified by Scrollable to be it's visible bounds instead of the application viewport bounds. This causes the Tooltip to position itself within these bounds.

I've added a builder to Tooltip to disable the positioning adjustment that ensures its always inside the viewport with snap_within_viewport(bool). I've then also removed the layer clip when drawing the tooltip so it's not clipped by the scrollable bounds (tooltip is effectively an overlay and should never be clipped).

Commit b3f5f74 shows the bug and 046e7e0 shows it being fixed. These commits can get dropped.

I realize this is a hacky solution, since snap_within_viewport shouldn't be something that's exposed or even considered and isn't really honest about why it's there. However, since we don't get the actual window viewport in the widget, we have no way of know when or when not to adjust to the viewport.

Should we do something like the following, so there is a window bounds that can be used that we know is unchanged during draw. Tooltip can then use this for it's positioning adjustment to the window bounds.

fn draw<'a>(
    &'a self,
    ...,
    viewport: &Rectangle,
    window: &'a Rectangle,
)

[hecrj]

Thanks! This should be good enough until we generalize our overlay support.