Add explicit IgnoreBOM and ErrorMode options to LibTextCodec decoders,
and thread them through TextDecoder and TextDecoderStream.
This lets Web-facing decoder APIs preserve BOMs when requested and use
fatal error handling without post-processing decoded output.
NB: RemoveBOM was renamed to IgnoreBOM as "RemoveBOM" is the name
used by encoding_rs and was previously an implementation detail.
The new name matches what is used by the encoding standard as it
is now also used in LibWeb.
Thread UTF-16 string input through JSON, script parsing, Date parsing,
Intl option parsing, Temporal parsing, and the helper library boundaries
that feed those parsers. Preserve ASCII fast paths where the source data
is known to be ASCII.
Move the remaining LibJS primitive string users to UTF-16 views and
strings. Remove the primitive string UTF-8 accessors and byte-string
coercion paths so new callers cannot rely on the old storage model.
Accept Utf16View patterns at the LibRegex compile boundary and pass
UTF-16 or ASCII storage directly into the Rust regex parser. This keeps
JavaScript regular expression construction from converting patterns
through UTF-8 when LibRegex can consume the same UTF-16 representation
used by LibJS.
Update RegExp construction, HTML pattern validation, the regex fuzzer,
and LibRegex tests to use the UTF-16 compile API.
