Let Qt Online Installer tell Creator the location of Ninja

1. Use the official Online Installer to install Qt for MSVC2019, Qt Creator, CMake and Ninja.
2. Start Creator.
   The installer configured kits using the installed Qt versions in Creator. These use CMake and Ninja. The location of CMake is properly configured.
3. Try to open a CMake-based example with one of the MSVC2019-based kits.
   Creator cannot open the project because it can't find Ninja.

This can be worked around by manually adding Ninja's location to the PATH variable in the kit settings. I think it would improve the out-of-the-box experience if that step wasn't necessary.