scriptc_ts7_json_value_end searched for the next quote again after each
backslash escape in a string, so a string with many escapes was scanned
once per escape. The quote it found now stays the candidate end until an
escape skips it, and each byte of a string is scanned once by each
search.
A test scans strings of 2,000,000 newline, backslash and quote escapes,
alone and inside an object, and compares the ends with jsonValueEnd's;
before the change it does not finish within 60 s.
Chris Tate
5e7338ad2c