Add code documentation of the API injection by JavaEEDependencyProcessor

JavaEEDependencyProcessor add various modules as deps to deployments. Add code documentation and probably a bit of code reorganization to make it clear to maintainers what this is about.

For example,

1) Some modules are added as deps to provide EE API support that does not require the backing of some other subsystem. Often other subsystems are involved in real-world use, but it is valid for a deployment to use these APIs independent of other subsystems.

2) The EE Concurrency APIs. If we had a different subsystem for EE concurrency those would go there, but we don't.

3) jakarta.resource.api, which might be an example of case #1, but doesn't feel like it and probably doesn't belong here but can be kept because it's too risky to remove it and not worth it given the small size (65K) of the added dep.