Introduce concept of byte strings and byte text blocks

[brandondahler]

Background

• What do these changes do?
  • Adds the ability to represent human-readable strings as properly encoded blob values
• Why are they important?
  • Blob shapes must be used in places where binary values are supported; however, the only option for representing blob values in the IDL have an inherently human unreadable representation -- base64 encoded strings.
  • In places we actually use blob literals, the value being used is often a human readable string that has been munged by the base64 encoding.
  • By adding these new byte string flavors, we can represent these potentially binary values as human readable strings in the IDL while keeping the same base64 encoding in the JSON AST.

Testing

• How did you test these changes?
  • Unit tests updated in several different areas.
  • Primarily found and replicated places where QUOTED_TEXT and TEXT_BLOCKs were being tested
  • Documentation updates were best effort -- I do not have an environment setup that is readily capable of building and inspecting the output.

Links

• Links to additional context, if necessary
• Implements Feature request: Support for human-readable blob values in the IDL #2852

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