RFR: 8087444: CornerRadii with different horizontal and vertical values treated as uniform

[Michael Strauß]

This PR fixes the incorrect computation of the `CornerRadii.uniform` flag for the 16-argument constructor.

I've also added tests for all other constructors.

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Commit messages:
 - fixed computation of uniform flag
 - failing test

Changes: https://git.openjdk.org/jfx/pull/1465/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1465&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8087444
  Stats: 82 lines in 2 files changed: 69 ins; 1 del; 12 mod
  Patch: https://git.openjdk.org/jfx/pull/1465.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1465/head:pull/1465

PR: https://git.openjdk.org/jfx/pull/1465