RFR: 8325900: Emit a warning on macOS if AWT has set the NSAppearance [v3]

[Michael Strauß]

> Platform preferences detection doesn't pick up effective macOS system preferences if AWT owns the NSApplication and has set its NSAppearance to a fixed value.
> 
> The workaround is to set the system property "apple.awt.application.appearance=system".
> 
> If this property is not set, the following warning will be emitted if a JavaFX application attempts to use the platform preferences API:
> 
> 
> WARNING: Reported preferences may not reflect the macOS system preferences unless the sytem
> property apple.awt.application.appearance=system is set. This warning can be disabled by
> setting javafx.preferences.suppressAppleAwtWarning=true.

Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:

  address review comments

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1367/files
  - new: https://git.openjdk.org/jfx/pull/1367/files/688b2f80..5c743df7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1367&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1367&range=01-02

  Stats: 15 lines in 2 files changed: 10 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1367.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1367/head:pull/1367

PR: https://git.openjdk.org/jfx/pull/1367