concurrencpp build failed with error C2039

[Cheney-W]

Hello, I'm a member of Microsoft VCPKG, when I built concurrencpp:x64-windows in an internal version of Visual Studio, it failed with following errors:
include\concurrencpp/threads/thread.h(23): error C2039: 'string': is not a member of 'std'

This issue caused by the STL PR: microsoft/STL#4633, and according to the recommendations of the STL developers, the affected files need to include the Standard <string> header.

I have applied this change in vcpkg by microsoft/vcpkg#39160. Since this VS internal version has not been released yet, I am submitting this issue just to inform you.