Feature #8508

Updated by Roel Standaert over 1 year ago

[C++ compiler and STL implementations are getting C++20 feature complete](, so we can look into replacing the `date` library with it. This would be especially nice on Windows, since using time zones on Windows would not require extra setup anymore. 

 This was I think this can be done in issue #8595 similarly to how we do `Wt::cpp17::any`: 

 - Have a CMake option to select the implementation, defaulting to the STL implementation if supported 
 - Introduce a `Wt::cpp20::chrono` namespace that is aliased to `std::chrono` or `date` 

 `WDate`, `WTime`, `WDateTime`, and `WLocalDateTime` may no longer be necessary. We could look into adding overrides in the right places, so that their use can be avoided if desired.