[windows] Comprehensive changes

- Qt5: Compile from source, upgrade to version 5.15.2
- ninja: upgrade to version 1.10.2
- cmake: upgrade to version 3.21.2
- llvm: add version 12.0.1, needed for vcpkg-tool
- vcpkg-tool: add/compile version 2021-08-12
- vcpkg: rebase on version 2021.05.12
- xtensor: dropped
- enabled long paths, needed for cleaning up Qt5 build tree