Check for invalid character escapes in regular expressions.
Parse \0 and \x00 and \u0000 in regular expressions.

Still doesn't match them, due to our use of zero-terminated strings.
Fix ToNumber from strings and parseInt and parseFloat.

Follow the spec more strictly, and don't rely on strtod's grammar.

GNU libc strtod accepts 0x prefixes, INF, INFINITY and much more which
we don't want, so pre-filter the string we pass to strtod.