Store parser errors, source range filenames, source code filenames,
module source, and Rust parser errors as UTF-16 where they flow back
into JavaScript-visible strings. Keep byte-oriented source buffers
byte-backed.
Remove temporary PrimitiveString, ByteString, and UTF-8 detours from
JSON, RegExp, module debug logging, print formatting, and tests.
The main streams AO file has gotten very large, and is a bit difficult
to navigate. In an effort to improve DX, this migrates WritableStream
AOs to their own file.