Implement SkPoint class & SkPathMeasure

[ErikSom]

Adding class implementation for SkPoint and SkPathMeasure.

I tried getting the SkPathMeasure to work with the following embind:

    value_array<SkPoint>("SkPoint")
        .element(&SkPoint::fX)
        .element(&SkPoint::fY);

But I kept on getting the error UnboundTypeError, Cannot call SkPathMeasure._getPosTan due to unbound types: 0x2c03
It seems when using a value_array as a raw pointer there are difficulties with properly binding the C++ types to their JavaScript equivalents.

I would also like to implement SkPathMeasure::getMatrix but this would also require binding the SkMatrix with class_<SkMatrix>, and before I do that I wanted to check in with you If I'm missing something or if this is the way to go.

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