RFR: 8257719: JFXPanel scene fails to render correctly on HiDPI after fix for JDK-8199592 [v2]

[Jose Pereda]

> This PR fixes a regression introduced in [JDK-8199592](https://bugs.openjdk.java.net/browse/JDK-8199592), where scene initialization was moved after updating output scales. However, in case of embedded windows (used by `JFXPanel` or `FXCanvas`), the scene has to be initialized before.
> 
> A test has been included. Before applying the fix, the JFXPanel is rendered with a garbled image, and after the fix, the rendering is correct.

Jose Pereda has updated the pull request incrementally with one additional commit since the last revision:

  Add new line at the end of the test file

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/364/files
  - new: https://git.openjdk.java.net/jfx/pull/364/files/8c81e317..4eb1ace5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=364&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=364&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/364.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/364/head:pull/364

PR: https://git.openjdk.java.net/jfx/pull/364