Normalized bounding polygon for text (that might not be aligned with
axis). Contains list of the corner points in clockwise order
starting from top-left corner. For example, for a rectangular
bounding box: When the text is horizontal it might look like: 0----1
| | 3----2
When it's clockwise rotated 180 degrees around the top-left corner
it becomes: 2----3 | | 1----0
and the vertex order will still be (0, 1, 2, 3). Note that values
can be less than 0, or greater than 1 due to trignometric
calculations for location of the box.