RFR: 8241840: Memoryleak: Closed focused Stages are not collected with Monocle. [v7]

[Florian Kirmaier]

> Closed focused Stages are not collected with Monocle
> 
> This commit adds a unit-test and a fix for collecting focused closed stages.
> 
> ticket: https://bugs.openjdk.java.net/browse/JDK-8241840

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

  JDK-8241840
  small formatting changes based on codereview

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/153/files
  - new: https://git.openjdk.java.net/jfx/pull/153/files/a7c9d83c..2971a112

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/153/webrev.06
 - incr: https://webrevs.openjdk.java.net/jfx/153/webrev.05-06

  Stats: 8 lines in 3 files changed: 0 ins; 3 del; 5 mod
  Patch: https://git.openjdk.java.net/jfx/pull/153.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/153/head:pull/153

PR: https://git.openjdk.java.net/jfx/pull/153