[12] RFR: JDK-8210092: Remove old javafx.swing implementation

[Kevin Rushforth]

Please review the following on GitHub:

https://bugs.openjdk.java.net/browse/JDK-8210092
https://github.com/javafxports/openjdk-jfx/pull/207
https://github.com/javafxports/openjdk-jfx/pull/207/files

This will remove the old JDK-10-based implementation of FX / Swing 
interop and cleanup the build to remove the legacy qualified exports and 
the logic that optionally excludes the new implementation. It also 
changes the dependency that javafx.swing has on jdk.unsupported.desktop 
from "requires static" (optional) to "requires", which will fix an 
existing bug with jlinked images that include javafx.swing.

-- Kevin