Type-check the list of child effects passed to SkMesh.

The child list passed into SkMesh::Make is now cross-checked against
the list of children from the SkMeshSpecification, and if they don't
agree, an error explaining the discrepancy is returned.

(If they _do_ agree, an error is also returned, because child-effect
support isn't actually implemented yet. But it's a different error.)

Change-Id: I0f27feda3310a03d3538892d5014a13c9274ab7c
Bug: b/40045302
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/760096
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
6 files changed