Previously only part of the preview would be visible when zoomed in,
with less visible the more you zoomed. This also now doesn't scale
the preview line thickness, similar to other image editing programs.
Lasso selection works by allowing the user to draw an arbitrary shape
much like the pen tool and ensuring the shape is closed by connecting
the start/end points when the user is done drawing. Everything inside
the shape becomes the selection.
Selection is determined via an outer flood fill. We begin a flood fill
from a point that is guaranteed to be outside of the drawn shape, and
anything the fill doesn't touch is determined to be the selection
region.
