Arcs don't normalize well

[rsheeter]

Observed when testing emoji clock faces with nanoemoji part files:

    {
      "normalized": "M0,0 a60 60 0 1 1 1,0 a60 60 0 1 1 -1,0 z",
      "shapes": [
        "M124,64 A60 60 0 1 1 4,64 A60 60 0 1 1 124,64 Z"
      ]
    },
    {
      "normalized": "M0,0 a48.1 48.1 0 1 1 1,0 a48.1 48.1 0 1 1 -1,0 z",
      "shapes": [
        "M112.14,64 A48.14 48.14 0 1 1 15.86,64 A48.14 48.14 0 1 1 112.14,64 Z"
      ]
    },

[rsheeter]

Interestingly fixing arc normalization doesn't alter the current implementation results for emoji, presumably because we hit arcs to cubics prior to reuse in the current model.