The javac tool now provides the ability to generate native headers as needed. This removes the need to run the javah tool as a separate step in the build pipeline. The feature is enabled in javac by using the new -h option, which is used to specify a directory in which the header files should be written. Header files will be generated for any class which has either native methods, or constant fields annotated with a new annotation of type java.lang.annotation.Native.

This should ease the transition to a modular build by allowing us to remove one extra javah step.

Note: the annotation is a noop with javah, it only affects 'javac -h'

There are two import removals - of "empty" generated headers from
M modules/javafx.graphics/src/main/native-glass/gtk/GlassApplication.cpp
M modules/javafx.graphics/src/main/native-prism-es2/PrismES2Defs.h