Defines all available line join styles as constants. Each line join style
is an instance of NamedValue. For use with HexaPDF::Content::GraphicsState#line_join_style.
See: PDF1.7 s220.127.116.11
The two segments are finished with butt caps and the space between the ends
is filled with a triangle.
The outer lines of the two segments continue until the meet at an angle.
An arc of a circle is drawn around the point where the segments meet.
Returns the argument normalized to a valid line join style.
0 or :miter can be used for the MITER_JOIN style.
1 or :round can be used for the ROUND_JOIN style.
2 or :bevel can be used for the BEVEL_JOIN style.
Otherwise an error is raised.