feat(firestore): add support for VectorValue

[Lyokone]

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[russellwheatley]

Other than some more test coverage + fixing CI, this LGTM 👍

[russellwheatley]

Might be worth adding e2e tests for potential edge cases, particularly for JS. For instance, not sure it would handle empty vector, single dimension, 2048 (maximum) dimensions, maximum dimensions + 1, very large values in vector, floats, negative values.