Implement ability to include module jars for preproc, completion, et al

[benfry]

It's not currently possible to use other JavaFX classes from the PDE, even when it's in use as a renderer: processing/processing4-javafx#15

We'll need to see how to include .jar files from the modules path for preprocessing and compilation. Once that's set, getting them working with runtime shouldn't be too much trouble.

[vsquared]

https://github.com/processing/processing4/blob/3185ebae15f1ee894a9a2a056cc253b4677012e3/java/src/processing/mode/java/JavaBuild.java line 1086. Would adding javafx.controls fix it? If you're going to include swing components you might as well add javafx controls.

[benfry]

That fixes one narrow problem regarding JavaFX (which is the cited example in the original post), but doesn't fix the broader issue. The broader issue is what this issue is about.

[vsquared]

What's wrong with adding all the modules:
"--add-modules", "javafx.base,javafx.graphics,javafx.swing,javafx.controls,javafx.fxml,javafx.media,javafx.web",

If that's a problem then consider adding a setting in Preferences to allow the user to choose the modules that they want to be included in JavaFX projects.