Fixes for GCP-9377 in retrieval methods of StandardVariableSummaries from the standard_variable_summary view:

* Handling of cross database soft references for standard variable "ontology star" components in local databases.
* Special handling for populating isA (class) relationships for differences in how it is handled in central v/s local databases: direct linkage in central, linked via Property in local !!
* Better handling of nulls in StandardVariableDao when mapping query results to the return object.

Additional unit tests for special handling scenario of local database standard variables.

Issue: GCP-9377
Reviewer: RebeccaB