[12] RFR: JDK-8210093: Build FX class files with -source 11 and -target 11

[Kevin Rushforth]

Please review the following on GitHub:

https://bugs.openjdk.java.net/browse/JDK-8210093
https://github.com/javafxports/openjdk-jfx/pull/208

This will start building the FX class files with "-source 11" and 
"-target 11" for JavaFX 12. It is dependent on JDK-8209966.

-- Kevin