Our floating point number parser was based on the fast_float library:
https://github.com/fastfloat/fast_float
However, our implementation only supports 8-bit characters. To support
UTF-16, we will need to be able to convert char16_t-based strings to
numbers as well. This works out-of-the-box with fast_float.
We can also use fast_float for integer parsing.
The rules for parsing integers don't specify an upper bound on the
value that can be returned, so the `parse_integer_digits` method can be
used to check whether the given arbitrarily-large StringView is valid
according to these rules. The `parse_integer` and
`parse_non_negative_integer` methods would fail for values larger than
2147483647 when they shouldn't have.