[structure view] main application package is not yet found for annotation declarations #1675
Description
If a project does not have a bean defined with @SpringBootApplication, but instead defines an annotation with @SpringBootApplication(as a library, for example), the corresponding root package of the project is not found (by the structure view and the modulith service), since they look for beans with that annotations only.
We need to capture all type and annotation declarations to identify all the elements that are annotated with @SpringBootApplication, keep those elements in the index and use that when looking for the root package of a project.