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.
Keep primitive string storage in Utf16String and remove the UTF-8
storage path from PrimitiveString. ASCII strings still use compact
Utf16String ASCII storage, while UTF-16 becomes the only owned
representation.
Our Temporal implementation is woefully out of date. The spec has been
so vastly rewritten that it is unfortunately not practical to update our
implementation in-place. Even just removing Temporal objects that were
removed from the spec, or updating any of the simpler remaining objects,
has proven to be a mess in previous attempts.
So, this removes our Temporal implementation. AOs used by other specs
are left intact.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
