[jfx11u] RFR: 8231558: [macos] Platform.exit causes assertion error on macOS 10.15 or later

[Ambarish Rapte]

This is clean backport.
Tested the patch in a [branch](https://github.com/arapte/jfx11u/tree/cherry-pick).
Backports tested in above branch are : 
[JDK-8264737](https://bugs.openjdk.java.net/browse/JDK-8264737), [JDK-8266860](https://bugs.openjdk.java.net/browse/JDK-8266860), [JDK-8267819](https://bugs.openjdk.java.net/browse/JDK-8267819), [JDK-8268219](https://bugs.openjdk.java.net/browse/JDK-8268219), [JDK-8231558](https://bugs.openjdk.java.net/browse/JDK-8231558),
[JDK-8268718](https://bugs.openjdk.java.net/browse/JDK-8268718), [JDK-8265400](https://bugs.openjdk.java.net/browse/JDK-8265400), [JDK-8267121](https://bugs.openjdk.java.net/browse/JDK-8267121), [JDK-8267858](https://bugs.openjdk.java.net/browse/JDK-8267858), [JDK-8267892](https://bugs.openjdk.java.net/browse/JDK-8267892)

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Commit messages:
 - 8231558: [macos] Platform.exit causes assertion error on macOS 10.15 or later

Changes: https://git.openjdk.java.net/jfx11u/pull/42/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=42&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8231558
  Stats: 208 lines in 7 files changed: 204 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/42.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/42/head:pull/42

PR: https://git.openjdk.java.net/jfx11u/pull/42