Provide ability for AbstractItdMetadataProvider to discover Java types for non-PhysicalTypeIdentifier notifications

Presently AbstractItdMetadataProvider does not support being notified of class-level notifications to be received unless the upstream dependency is a PhysicalTypeIdentifier.

A fallback model should apply where a class-level notification is received that does not have a PhysicalTypeIdentifier upstream dependency. The fallback will be to locate all *.java files in the file system and request the subclass provide the metadata.

In practical terms this allows the subclass to be notified of project-wide metadata changes such as:

metadataDependencyRegistry.registerDependency(ProjectMetadata.getProjectIdentifier(), getProvidesType());