RFR: 8289587: IllegalArgumentException: Color.rgb's red parameter (-16776961) expects color values 0-255

[Jose Pereda]

This PR solves an IAE exception that happens when invoking a ColorChooser control within a WebView, by getting the r, g, b values from the Color before calling the colorChooser.

A system test is included, to verify that there is no exception and the two native functions that are modified produce the expected color components.

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Commit messages:
 - Get rgb values from color before calling colorChooser, including test

Changes: https://git.openjdk.org/jfx/pull/809/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=809&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289587
  Stats: 184 lines in 3 files changed: 178 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jfx/pull/809.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/809/head:pull/809

PR: https://git.openjdk.org/jfx/pull/809