Overloads for strings in ascii.h

[dimo414]

Several functions in ascii.h, such as the ascii_is*() functions, operate on characters but not strings. Most of these functions would be meaningful on strings too, e.g. to express that a string consists entirely of a given ASCII subset.

I just added this to my codebase, but it feels like Abseil could reasonably provide this alongside the char functions:

bool IsStringPrintableAscii(std::string_view s) {
  return std::all_of(s.begin(), s.end(), [](unsigned char c) { return absl::ascii_isprint(c); });
}

FWIW this was motivated by grpc/grpc#34798 - gRPC requires callers ensure their metadata strings are printable ASCII, but (AFAICT) does not provide an API to validate this.