Fix Bug with Ion Text<>Binary Conversion

[rmarrowstone]

This change fixes a bug in the Ion Text<>Binary conversion where an Ion stream of multiple top-level values would be transcoded as an Ion list.

In the process of fixing it I cleaned up all of the Format comparisons to be identity of enum constant instead of string comparison of value. This is a lot more succinct and avoid helps to avoid typo errors.

Issue #, if available:

Description of changes:

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