This PR implements a CMake + ninja build farm setup for the most common compilers used on modern versions of Windows.

Both - developer -focused and CI/CD pipeline -focused, to cover the following compilers:

• Visual Studio 2015 (v140) - C++11/C++14 - targeting Windows 8.1 SDK and above.
• Visual Studio 2017 (v141) - C++17 - targeting Windows 10 and above.
• Visual Studio 2019 (v142) - C++20 - targeting Windows 10 and above.
• LLVM Clang - targeting whatever version of Windows SDK. Tested with 11 and 12.

Using the following build systems:

• CMake
• Ninja - fastest, with optional fallback to MSBuild.
• vcpkg - used for dependency management.

The process is largely documented here . Except that now we also support not only 2019. But older compilers too, plus LLVM Clang which we never had in our build system for Windows. Ad-hoc tested that the code works well with Clang-11 and Clang-12. This comes in handy, because things like Chromium on Windows - build with clang.

Build scripts contain enough comments for further customization and tweaking as-necessary. Someone implementing their own custom build pipeline may use these scripts as a reference example. Devs may also use these scripts to quickly build and test the SDK side-by-side with a set of different compilers installed on one box. Output from the build is laid out as follows:

Running something like:

tools\build-vs2015.cmd
tools\build-vs2017.cmd
tools\build-vs2019.cmd
tools\build-clang-12.cmd

Produces a set of build artifacts in one run:

• nostd classes - for ABI compat across different compilers.
• WITH_STL - for static linking, with native STL classes.
  for all compilers above.

Note that vcpkg installation for Visual Studio 2015 must always be stored separately from the rest. Because if you use vs2019 to compile and link vcpkg libraries -- these packages won't link to SDK being built with vs2015 compiler and linker. That limitation described in Visual Studio compiler documentation here :