Converts specific types to Uint8Array chunks.

• string is converted to utf-8, concatenating a trailing lf
• string[] each item in the array is converted to utf-8, adding a trailing lf, all concatenated to a single Uint8Array
• Uint8Array is passed on unchanged
• Uint8Array[] is concatenated to a single Uint8Array

Strings are always treated as lines, and we add a trailing lf character. Data in byte form is always treated strictly as binary data.