RFR: 8324239: JFXPanelHiDPITest fails on Windows 11

[Prasanta Sadhukhan]

Test fails with

JFXPanelHiDPITest > testScale FAILED
    java.lang.NullPointerException: Cannot invoke "java.awt.image.BufferedImage.getWidth()" because "pixelsIm" is null 

because scenePeer is not yet created as the test is run with invokeLater.
FIx is to make it run with invokeAndWait so that it waits for the scene to be created..

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Commit messages:
 - 8324239: JFXPanelHiDPITest fails on Windows 11

Changes: https://git.openjdk.org/jfx/pull/1344/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1344&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324239
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1344.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1344/head:pull/1344

PR: https://git.openjdk.org/jfx/pull/1344