Implement the six WTF::charactersToDouble and WTF::charactersToFloat
overloads for Latin-1 and UTF-16 input and the four static
WTF::double_conversion::StringToDoubleConverter StringToDouble and
StringToFloat overloads for char and uint16_t input, following pinned
public WebKit. One parser follows StringToIeee: the number grammar, the
772-digit cut with a sticky digit, the exponent saturation and the
processed length. charactersToDouble and charactersToFloat add
toDoubleType's leading ASCII spaces and ok/parsedLength results, map
UTF-16 code units above 0x7F to 0 and round the float overloads through
double. StringToDoubleConverter reads the code units as they are, skips
no spaces and rounds StringToFloat directly to float as Strtof does.
Null characters with a nonzero length and a null processed length throw
where WebKit faults, a decimal exponent that leaves the range of
WebKit's int throws where WebKit overflows, and a UTF-16 charactersTo*
length above UINT32_MAX throws where WebKit's conversion Vector crashes.
