remove dependencies on internal API's of core modules

[johanvos]

At this moment, it is not possible to build the JavaFX modules with a JDK that doesn't have JavaFX as bootJDK.
The following issue on JBS tracks this: https://bugs.openjdk.java.net/browse/JDK-8195798

In particular, the following issue tracks the removal of the dependencies on the internal logging API:
https://bugs.openjdk.java.net/browse/JDK-8195799

Reviewing this code is highly encouraged.

[johanvos]

The umbrella issue for this is https://bugs.openjdk.java.net/browse/JDK-8195798

[kevinrushforth]

By way of cleanup, I note that since https://bugs.openjdk.java.net/browse/JDK-8195798 is resolved, this issue can be closed, too.