Well-defined encoding of test input data

[RCHowell]

As PartiQL evolves to have a containerized Ion type (a'la variant('ion')) we must define the canonical encoding of PartiQL values which the conformance test may/may not use.

Currently we a partiql value encoding in Ion using the de-facto standard, but we must be careful to not treat this as back-ticked Ion (aka variant).

The partiql-lang-kotlin test runner depends on a "PartiQL Value Reader" which understands the "PartiQL Encoded as Ion" representation.

Related

• https://github.com/orgs/partiql/discussions/92
• [V1] Replace PartiQLValue with Datum partiql-lang-kotlin#1602