* Add missing includes.
* Add libc++ < 20 fallback for floating-point strToNumber
libc++ prior to version 20 does not implement std::from_chars for
floating point types, which causes builds to fail on systems using older
libc++ versions (e.g. FreeBSD).
Add a small fallback using strtof/strtod/strtold for building with
libc++ < 20.
While libstdc++, or libc++ 20 or later continue to use the existing
std::from_chars implementation, this change restores compatibility with
older libc++ versions.
