[query] Support VCF v4.5

[chrisvittal]

VCF version 4.5 contains the changes we developed as part of our work developing the Scalable Variant Call Representation.

As the developers and drivers of these changes, we should fully support v4.5 via import to VDS and export from VDS.

Current checklist. May be extended over time:

• Prefer LEN over END for reference blocks. (Begins in [query/vds] Add LEN field to VDS  #14675)
• Update the combiner to convert to LEN from INFO END (Part of [query/vds] Add LEN field to VDS  #14675).
• Update to_dense_mt to use LEN (we think it may be more efficient).
• Add VDS to VCF export.
• Add Sparse VCF to VDS import.
• 'Official' non-ref genotype <*> support?