RFR: 8351867: No UI changes while iconified

[John Hendrikx]

Adds code to trigger a scene update when a Window is restored

This seems to solve https://bugs.openjdk.org/browse/JDK-8351867 and https://bugs.openjdk.org/browse/JDK-8146479

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Commit messages:
 - Ensure a redraw is performed after windows is restored

Changes: https://git.openjdk.org/jfx/pull/1733/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1733&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351867
  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1733.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1733/head:pull/1733

PR: https://git.openjdk.org/jfx/pull/1733