RFR: 8263322: Deadlock when calling Application.launch in the FXThread after Platform.startup [v3]

[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
   removed unused imports, added missing change
 - JDK-8263322
   Updated the unit-test so they match the wanted behavior discussed in the PR
 - JDK-8263322
   Added the tests for both cases, when JavaFX was initialized with Application.launch and Platform.startup

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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/6abe618e..0abc71e0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=421&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=421&range=01-02

  Stats: 307 lines in 5 files changed: 200 ins; 106 del; 1 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