Primarily driven by a wish to increase performance of parsing .cube
files. But the functions that are added or changed are used across
parsing of all/most of text based formats.

With these changes, parsing "Khronos PBR Neutral" .cube file (5.4MB)
on Ryzen 5950X / VS2022 Release build: 167ms -> 123ms.

- Add locale independent IsSpace(char). Somewhat similar to 3aab90d,
  whitespace trimming perhaps should not be locale dependent.
- Add IsEmptyOrWhiteSpace() and use that inside ParseUtils::nextline,
  instead of doing Trim(line).empty().
- Add StringUtils::StartsWith(char) and use that in various parsers
  that were constructing whole std::string object just to check for a
  single character.
- When building for C++17 or later, NumberUtils can use standard
  <charconv> from_chars functions (except on Apple platforms, where
  those are not implemented for floating point types as of Xcode 15).
  This has advantage of not having to deal with errno or locales. Saves
  some thread local storage accesses and function calls (e.g. on Windows
  errno is actually a function call).
- There's a CMake setup change that adds /Zc:__cplusplus flag for MSVC;
  for backwards compat reasons it does not report proper C++ version
  detection defines otherwise.

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>

Currently it was only tested indirectly via XMLReaderUtils_tests and
file format tests

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>

…kip optional whitespace

To match the pre-C++17 behavior that was there before

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>

Signed-off-by: Aras Pranckevicius <aras@nesnausk.org>