VS: Make CMAKE_GENERATOR_INSTANCE usable without VS Installer On Windows and Wine, both the COM interface and `vswhere` might not be available. `CMAKE_GENERATOR_INSTANCE` is still supposed to work since commit 195d47e213 (VS: Allow CMAKE_GENERATOR_INSTANCE to specify portable instance, 2021-10-21, v3.23.0-rc1~452^2). Issue: #21639