Produce JS-visible string results as UTF-16 at their source, including
numeric formatting, BigInt and BigFraction formatting, URI encoding,
console formatting, parser errors, regular expression errors, Intl and
Temporal records, LibUnicode locale boundaries, and LibWeb bindings.
Handle fractional radix formatting through the UTF-16 builder view.
Add Core::TimeZone as the single entry point for changing the
current time zone. This updates both ICU and the process TZ/tzset
state so libc-backed helpers such as AK::UnixDateTime::to_string()
agree with JS/ICU time zone state. Previously only the ICU timezone
would be updated, which could result in inconsistent results being
returned.