Use Ninja for packaging on Windows

[steven-johnson]

Due to an apparent bug in CMake 3.18, we can't use Ninja to drive Multi-Config packaging, and must use MSBuild instead. This is gross and inconvenient. This is a tracking bug to verify we switch to Ninja there if/when possible.

[alexreinking]

I will investigate & minimize after my CppCon talk.

[steven-johnson]

Presumably we can fix this once #6910 lands (the relevant comment at master.cfg:912 indicates the bug is in CMake 3.18)?

[alexreinking]

I hope so! It looks like some of the issues I had opened related to this have been closed since I last checked:

https://gitlab.kitware.com/cmake/cmake/-/issues/22023 (still open, but maybe not a blocker)
https://gitlab.kitware.com/cmake/cmake/-/issues/21973 (fixed in 3.20, was a blocker)
https://gitlab.kitware.com/cmake/cmake/-/issues/21982 (still open, but maybe not a blocker)
https://gitlab.kitware.com/cmake/cmake/-/issues/21983 (fixed in 3.22, but comments are concerning, was a blocker)