Support for multiple file configs for each applicable attribute

[sgammon]

Since GraalVM's original rule set, new support has dropped: now, a user can add multiple configurations in several cases (JNI, reflection, resources), and GraalVM will merge these before applying.

Unfortunately, our existing attributes assume just one file input for each of these. We should add alternative attributes which allow specifying more than one config for each. Later, it might be worth deprecating the older attributes.

Alternatives to consider: Do we need this if the user can wrap the configurations in a filegroup themselves?