RFR: 8326619: Stage.sizeToScene() on maximized/fullscreen Stage breaks the Window [v4]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Implement isSizeToSceneAllowed() method to determines whether the sizeToScene() request is allowed. Implement much more tests
 - Merge branch 'master' of https://github.com/openjdk/jfx into jdk-8326619-maximize-minimize-scene
 - improve tests
 - JDK-8326619: Improve tests
 - JDK-8326619: Stage.sizeToScene() on maximized/fullscreen Stage breaks the Window

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1382/files
  - new: https://git.openjdk.org/jfx/pull/1382/files/e58a2fda..eeab0fa8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1382&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1382&range=02-03

  Stats: 88862 lines in 1197 files changed: 47740 ins; 21303 del; 19819 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