Transforms an ExternalNodeAssociation (IssueComponent) based on the project import mapper that is provided. This should only be
used with a fully mapped and validated ProjectImportMapper.
projectImportMapper - a fully mapped and validated ProjectImportMapper
component - the external node association that contains all the old values that need to be transformed and other values
that should be stored that need no transformation.
a new ExternalNodeAssociation that contains the transformed values based on the projectImportMapper. Null
if the node association type is not a component type or if the issue or component id's have not been mapped.