Generate and store location.sequence and sequenceReference.moleculeType, and include in object responses

[jsstevenson]

These are ~objectively determinable and can be helpful to include in an object response

[theferrit32]

I think the percentage of the time that, given a VRS variation, you will want to know the location.sequence and sequenceReference.moleculeType, is high enough that we should always include it even though it is derivable and not part of the identity of the object.

Especially since we will almost certainly have had to derive it during the processing of the input variation (and then discarded it).

[korikuzma]

Related VRS-Python discussion: ga4gh/vrs-python#564

We include the sequence in the Variation Normalizer output and have an open issue for moleculeType (cancervariants/variation-normalization#594). It'd be nice to have this (either annotator mode, helper methods, or whatever we decide) in VRS-Python so we can reuse in both apps.

[jsstevenson]

This is also very cacheable, especially for genomic sequences