RFR: 8310885: Width/height of window is not set after calling sizeToScene

[Guillaume Tâche]

`setHeight()` / `setWidth()` were ignored if called after `sizeToScene()` and before `show()`.      
Now the `sizeToScene` flag is unset in these methods to ensure the right values are set when the window is shown.

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Commit messages:
 - 8310885: Width/height of window is not set after calling sizeToScene

Changes: https://git.openjdk.org/jfx/pull/1195/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1195&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310885
  Stats: 68 lines in 2 files changed: 62 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1195.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1195/head:pull/1195

PR: https://git.openjdk.org/jfx/pull/1195