lint: add mising isolates and minor style fixes
string_bytes: implement new v8 API

v8 has a new API to write out strings to memory. This has been
implemented.

One other change of note is BINARY encoded strings have a new
implementation. This has improved performance substantially.
string_bytes: use external for large strings

When large strings are used they cause v8's GC to spend a lot more time
cleaning up. In these cases it's much faster to use external string
resources.

Utf8 strings do not use external string resources because only one and
two byte external strings are supported.

EXTERN_APEX is the value at which v8's GC overtakes performance.