ENSCORESW-3212: Backport HGNCParser

Created by: tgrego

Description

Port changes made to HGNCParser in ensembl-xref, including unit tests, back to ensembl:feature/xref_sprint.

Use case

See ENSCORESW-3212

Benefits

Salvage more work from the xref sprint.

Possible Drawbacks

Increased test-suite run time. MultiTestDB has been duplicated for misc-scripts/xref_mapping/t

Testing

Have you added/modified unit tests to test the changes?

yes

If so, do the tests pass/fail?

pass

Have you run the entire test suite and no regression was detected?

yes