RFR: 8263322: Deadlock when calling Application.launch in the FXThread after Platform.startup [v2]

[Florian Kirmaier]

> Fixing deadlock when calling Application.launch in the FXThread after Platform.startup

Florian Kirmaier has updated the pull request incrementally with three additional commits since the last revision:

 - JDK-8263322
   Added missing change
 - JDK-8263322
   Small changes based on code review
 - JDK-8263322
   Small changes based on code review

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/421/files
  - new: https://git.openjdk.java.net/jfx/pull/421/files/9a70d349..6abe618e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=421&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=421&range=00-01

  Stats: 195 lines in 3 files changed: 109 ins; 84 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/421.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/421/head:pull/421

PR: https://git.openjdk.java.net/jfx/pull/421