Get sketchbook location from Processing

[mingness]

Describe the feature or enhancement

Currently the sketchbook location is inferred from the OS. It could instead be taken from an installation of Processing.

From @Stefterv :
Take a look at the getSettingsFolder() functions in the different platforms: https://github.com/processing/processing4/tree/main/app/src/processing/app/platform

The best approach would be to look at the sketchbook.path.four in the prefrences.txt the sketchbook location can be dynamic based on that

What is the use case?

If the user wishes to test their new library in Processing, they will need to locally install it by accessing the sketchbook folder.

Alternatives considered

The current implementation is via OS and testing of folder existence.