Backport 3306: Clip: Fix edgeInterpolationIndexToUnique creation bug

Vicente Bolearequested to merge
vbolea/vtk-m:backport-3306 into release

Backport of !3306 (merged)

This is the correct order:

  1. Copy the existing edges (which include duplicates)
  2. Sort the copies edges
  3. Remove the duplicate edges from the copied edges so that they are unique
  4. Create a edgeInterpolationIndexToUnique map by querying each edge (including duplicates) and find the which unique id they have by looking into the unique copied edges

(cherry picked from commit 0cbc72eb)

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