[Cuda] Simplify and optimise the getMaxRegistersJitOptionValue utility

[GeorgeWeb]

This change simplifies the getMaxRegistersJitOptionValue function as it was previously unclear what the return bool value actually meant, because it doesn't really signify whether the value was valid or not but it was more of a whether the parsing was successful. Instead, we now just return the parsed value if it is successfully parsed, otherwise we return the default.
Additionally, we replace the use of std::stoi with std::from_chars which is much lighter weight (and works well with std::string_views), in order to avoid extra dynamic allocation(s).