RFR: JDK-8326619: Stage.sizeToScene() on maximized/fullscreen Stage breaks the Window

[Marius Hanl]

This PR fixes the problem that maximizing/fullscreen a `Stage` or `Dialog` is broken when `sizeToScene()` was called before or after.

The approach here is to ignore the `sizeToScene()` request when the `Stage` is maximized or set to fullscreen. 
Otherwise the Window Manager of the OS will be confused and you will get weird flickering or wrong Window buttons (e.g. on Windows, the 'Maximize' button still shows the 'Restore' Icon, while we already resized the `Stage` to not be maximized).

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Commit messages:
 - JDK-8326619: Stage.sizeToScene() on maximized/fullscreen Stage breaks the Window

Changes: https://git.openjdk.org/jfx/pull/1382/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1382&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326619
  Stats: 179 lines in 3 files changed: 179 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1382.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1382/head:pull/1382

PR: https://git.openjdk.org/jfx/pull/1382