Release v4.13.0-rc1-patched-snapshot_2020-08-24

QtCreator patches:

• use patched qbs for Windows build
• use "c++2a" (gcc/clang) / "c++latest" (msvc) from qbs for clang code model

qbs 1.17 patches:

• cxxLanguageVersion: "c++2a" is allowed. Note: It will trigger "c++latest" for msvc
• visual studio (msbuild) project generation is more usable (still opinionated)