feat: minor API improvements

[mattjohnsonpint]

Description

Some API improvements and other misc changes that have been accumulating locally, now ready for publishing.

Highlights:

• Use correct terminology "connection" instead of "host" everywhere, to align with manifest change made long ago.
• Update AssemblyScript to latest version 0.27.34 which adds:
  • support for rest params, simplifying a few of our APIs
  • corrects output from f32.toString, improving vector arrays represented in JSON
• Dgraph API improvements:
  • closer alignment between Go and AssemblyScript SDKs by adding constructor functions in the Go SDK, and fluent APIs for setting variables and configuring mutations to both SDKs.
  • deprecate execute (which takes a Request object) in favor of executeQuery and executeMutations which work directly with Query and Mutation objects. See updated Dgraph examples for how this drastically simplifies user code.
  • add EscapeRDF function and update examples, to properly escape string values in Nquad mutations
• HTTP API improvements:
  • Add missing Bytes method for content, request, and response - to align with HTTP fetch API.
  • Use Uint8Array instead of ArrayBuffer where appropriate in AssemblyScript
  • Update Json method for content, request, and response to return an error instead of panicking, in Go.
• OpenAI model API improvements:
  • Support direct passing of pre-encoded base64 strings for audio and image content, to avoid having to decode and re-encode the same data in certain cases.

Checklist

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• I have manually tested the new or modified code, and it appears to behave correctly.
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