fix cube performance

[pca006132]

Removed the need for using transforms and AsOriginal for cube, which improves performance quite a bit.
Closes #710.

@elalish do you know why MeshGLRoundTrip now breaks?

TEST(Boolean, MeshGLRoundTrip) {
  Manifold cube = Manifold::Cube(glm::vec3(2));
  ASSERT_GE(cube.OriginalID(), 0);
  const MeshGL original = cube.GetMeshGL();

  Manifold result = cube + cube.Translate({1, 1, 0});

  ASSERT_LT(result.OriginalID(), 0);
  ExpectMeshes(result, {{18, 32}});
  RelatedGL(result, {original});

  MeshGL inGL = result.GetMeshGL();
  ASSERT_EQ(inGL.runOriginalID.size(), 2);
  const Manifold result2(inGL);

  ASSERT_LT(result2.OriginalID(), 0);
  ExpectMeshes(result2, {{16, 28}}); // <--- need this to pass the test
  RelatedGL(result2, {original});

  const MeshGL outGL = result2.GetMeshGL();
  ASSERT_EQ(outGL.runOriginalID.size(), 2);
}

I assume it simplifies the mesh when manifold is created from the MeshGL, but I have no idea why it does this. Changing cube to Manifold::Cube(glm::vec3(2)).AsOriginal() doesn't help.

[elalish]

Hmm, that's odd. I almost wonder if the test was broken before? I feel like both ExpectMeshes calls should ask for {16, 28}. Does that fix it? What are we actually getting for result and result2?

[pca006132]

result = {18, 32}, result2 = {16, 28}, thinking about it {16, 28} makes more sense, we union two identical cubes, the mesh should be simplified.

[pca006132]

@elalish what do you think about the value of result? I feel that {16, 28} makes more sense but somehow we are not getting that...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0b7ee87) 91.67% compared to head (db7b635) 91.69%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #717      +/-   ##
==========================================
+ Coverage   91.67%   91.69%   +0.01%     
==========================================
  Files          37       37              
  Lines        4732     4730       -2     
==========================================
- Hits         4338     4337       -1     
+ Misses        394      393       -1     

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[elalish]

Thanks, that test looks better now!