MergePaths causes warping when paths overlap

[jzbrooks]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Shrinking this vector drawable results in the image being hollowed out.

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="19dp"
    android:height="30dp"
    android:viewportWidth="19"
    android:viewportHeight="30">
  <path
      android:pathData="M18.4271,7.7715C17.7591,2.6885 14.5931,0.0015 9.2721,0.0005C3.9521,0.0015 0.7861,2.6885 0.1171,7.7715C-0.1029,9.4425 -0.0129,11.2385 0.3831,13.1085C2.3331,22.3275 7.0441,27.8595 8.4421,29.3365C8.6571,29.5625 8.9601,29.6925 9.2721,29.6935C9.5851,29.6925 9.8871,29.5625 10.1031,29.3365C11.5001,27.8595 16.2121,22.3275 18.1621,13.1085C18.5581,11.2385 18.6471,9.4425 18.4271,7.7715"
      android:fillColor="#253993"
      android:fillType="nonZero"
      />
  <path
      android:pathData="M16.5721,12.7755C14.8421,20.9505 10.7491,26.1695 9.2721,27.8385C7.7961,26.1695 3.7031,20.9505 1.9731,12.7755C1.6141,11.0815 1.5321,9.4685 1.7281,7.9825C2.2841,3.7615 4.8221,1.6215 9.2721,1.6205C13.7221,1.6215 16.2601,3.7615 16.8161,7.9825C17.0121,9.4685 16.9301,11.0815 16.5721,12.7755"
      android:fillColor="#253993"
      android:fillType="nonZero"
      />
</vector>

Expected behavior
The image to visually identical

Screenshots

[jzbrooks]

svgo had a similar bug: svg/svgo@e1060df
The ultimate solution is probably to revert #59 and implement intersection checking.

[jzbrooks]

https://computerwebsite.net/writing/gjk seems like a useful summary of the algorithm they use

[jzbrooks]

It just occurred to me that GJK isn't absolutely necessary. A good first step would be to use an axis-aligned bounding box check for intersection detection. svgo does this as an optimization but it's really all that's required to avoid this bug because it will over signal intersections. GJK would make the intersection detection more precise and result in more path merging, but it could be done in a follow up.

[jzbrooks]

https://www.w3.org/TR/SVG11/implnote.html#ArcParameterizationAlternatives

and specifically https://www.w3.org/TR/SVG11/implnote.html#ArcConversionEndpointToCenter seems helpful