Implement support for handling Java “modules” and clean up JavaFX-specific workarounds

Created by: benfry

JavaFX 16 (which we're using as of 4.0 alpha 5) is bundled as a set of Java “modules,” rather than regular .jar files. As such, it will complain if the code is loaded from the usual CLASSPATH.

For now, there are some workarounds in the build process that treat the (newly separated) JavaFX library as a special case, but this is pretty gross, and we need to either:

1. Start tracking a modulesPath and module lists during build and bundling so that it can be specified when running from the PDE and when exporting.
2. Alternatively, we could add additional information to library.properties so that special command line options can be added. In this case, it would be --add-modules javax.base, etc, but could also be used to cover -XstartOnFirstThread for libraries that require that (LWJGL?)

Start by tracing the build and bundling process for JavaFX 16 modules, including how the PDE runs projects and how exports are assembled. Compare the proposed modulesPath/module-list approach with adding command-line options through library.properties. Done means JavaFX modules work without the current special-case workarounds in both PDE runs and exports.