RFR: 8257618 Lanai: GradientPaint interpolates over stops limits

[Alexey Ushakov]

Limit interpolation parameter
Added LINEAR_RGB->sRGB if necessary

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Commit messages:
 - 8257618 Lanai: GradientPaint interpolates over stops limits

Changes: https://git.openjdk.java.net/lanai/pull/138/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=138&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257618
  Stats: 41 lines in 4 files changed: 36 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/lanai/pull/138.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/138/head:pull/138

PR: https://git.openjdk.java.net/lanai/pull/138