[8u] RFR 8231438 [macos] The dark mode is not supported yet

[Sergey Bylokhov]

Hello,

Please review the backport of JDK-8231438 to 8u.

JBS: https://bugs.openjdk.java.net/browse/JDK-8231438
jdk8u patch: http://cr.openjdk.java.net/~serb/8231438/jdk8u-dev/webrev.00/
jdk14 patch: http://hg.openjdk.java.net/jdk/jdk14/rev/dae610645225
jdk14 review: https://mail.openjdk.java.net/pipermail/awt-dev/2019-September/015420.html

If anybody started to use SDK 10.14+ to build JDK, this automatically opt-in support of dark mode:
--------------
"The system assumes that apps linked against the macOS 10.14 or later SDK support both light and 
dark appearances"
https://developer.apple.com/documentation/appkit/nsappearancecustomization/choosing_a_specific_appearance_for_your_macos_app?language=objc
--------------

Unfortunately the dark mode still unsupported by the AWT/Swing, for a few reasons, example:
https://bugs.openjdk.java.net/browse/JDK-8228555
Until the bugs related to the dark mode are not fixed we should opt-out it.

See the link above to review request for the jdk14 for an additional information.

The patch does not apply clean, I had to ifdef it only for the sdk 10.14+, so the change will not 
break the build using old xcode(before sdk 10.9), note that I cannot test the old xcode myself, can 
somebody verify it?

-- 
Best regards, Sergey.