RFR: 8259653: Multistop gradients incorrectly works with non uniform stops

[Alexey Ushakov]

Correctly handled uniforms.fract parameters. Removed duplication

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Commit messages:
 - 8259653: Multistop gradients incorrectly works with non uniform stops

Changes: https://git.openjdk.java.net/lanai/pull/152/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=152&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259653
  Stats: 186 lines in 1 file changed: 43 ins; 136 del; 7 mod
  Patch: https://git.openjdk.java.net/lanai/pull/152.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/152/head:pull/152

PR: https://git.openjdk.java.net/lanai/pull/152