By a quick look on the buildfarm we seem to use Ninja >= 1.11.1. However since Meson can use both Ninja and VS as a backend I'm not certain which section would be most appropriate for naming the minimal required version of Ninja.
When I tried building with the VS backend it blew up, I don't recall the details. I think we should just use ninja everywhere. That keeps things simple. On Windows I just install python and then do "pip install meson ninja"