RFR: 8269907 memory leak - Dirty Nodes / Parent removed [v3]

[Florian Kirmaier]

> After thinking about this issue for some time, I've now got a solution.
> I know put the scene in the state it is, before is was shown, when the dirtyNodes are unset, the whole scene is basically considered dirty. 
> This has the drawback of rerendering, whenever a window is "reshown", but it restores sanity about memory behaviour, which should be considered more important.

Florian Kirmaier has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8269907
  We now require the rendering lock when cleaning up dirty nodes. To do so, we moved some code required for snapshot into a reusable method.

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/584/files
  - new: https://git.openjdk.java.net/jfx/pull/584/files/c603d2b1..28b793b5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=584&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=584&range=01-02

  Stats: 7 lines in 1 file changed: 5 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/584.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/584/head:pull/584

PR: https://git.openjdk.java.net/jfx/pull/584