RFR: JDK-8326619: Stage.sizeToScene() on maximized/fullscreen Stage breaks the Window [v2]

[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).

Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8326619: Improve tests

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1382/files
  - new: https://git.openjdk.org/jfx/pull/1382/files/bc607409..bbdb4db7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1382&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1382&range=00-01

  Stats: 22 lines in 2 files changed: 5 ins; 2 del; 15 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