Provide a standardized way to handle the C++ "standard" headers
customized to be used with current CMake C++ standard constraints.
Offer under directory `cm` headers which can be used as direct
replacements of the standard ones. For example:
#include <cm/string_view>
can be used safely for CMake development in place of the `<string_view>`
standard header.
Fixes: #19491
This adds the following functions to cmStringAlgorithms:
- `cmStrToLong`: moved from `cmSystemTools::StringToLong`
- `cmStrToULong`: moved from `cmSystemTools::StringToULong`
Overloads of the given functions for `std::string` are added as well.
