Function is_alpha

test-app/runtime/src/main/cpp/ada/ada.h:1036–1038

constexpr char to_lower(char x) noexcept { return (x | 0x20); }

constexpr bool is_alpha(char x) noexcept {
  return (to_lower(x) >= 'a') && (to_lower(x) <= 'z');
}

constexpr bool is_windows_drive_letter(std::string_view input) noexcept {
  return input.size() >= 2 &&