Shape updates

[davepagurek]

Some implementations previously missing, brought up again by @GregStanton here: #1 (comment)

• Maps the old curve() to the new spline() (changed in Minor 2.0 shape changes p5.js#7656)
• Puts back public beginGeometry/endGeometry methods (hidden in favor of buildGeometry for API clarity; they still exist internally in the renderer as part of the internal implementation, so we can just expose them again here)
• Adds an approximate mapping of the old curveDetail and bezierDetail to the new curveDetail. It's not super feasible in an addon to fully restore the old behaviour fully, so this has the following compromises:
  • It sets the sampling density based on an assumed average curve length, since we can't easily access the actual length of each curve. I'm using a third of the diagonal of the canvas size.
  • There's still only one detail under the hood; code that tries to use two separate details (which at least seems uncommon in practice) will end up overwriting the same singular detail