feat: add support for multi select hash to JMESPath visitor

[0marperez]

Issue \

closes #930

Description of changes

• Added support for multi select hash
• Added missing list from multi select list to match JMESPath syntax
• ensureNullGuard is now addNullGuard and is added to all temporary val's
• subField function now allows accessing members of shapes that "are not there" (multi select hash creates anonymous objects with arbitrary attributes that don't show up in the model)
• comparator for anyStringEquals and allStringEquals now casts to a list of strings before comparing (anonymous objects have attributes of generic type)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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