Java: Add Import.getATypeImport

[Marcono1234]

When working with Javadoc it is often necessary to find out to which type a Javadoc tag refers to. Imports are one way to find this out, however the QL Import class does not define a common predicate to get an imported type despite all import types being able to import types in some way.
It would therefore be useful to add a predicate Import.getATypeImport() which would behave like this:

• ImportType: getImportedType()
• ImportStaticTypeMember: getATypeImport()
• ImportOnDemandFromPackage: getAnImport()
• ImportOnDemandFromType: getAnImport()
• ImportStaticOnDemand: getATypeImport()

Edit: As described by #10498 instead of adding this predicate, it might make more sense to have a predicate for CompilationUnit which obtains a type which is available by its simple same in that compilation unit.