[TEST] Move to conan 2.0

[trisyoungs]

This PR moves us to Conan 2. Progress so far:

1. Conan2 CMake integration is "better" but forces us back to a static conanfile.txt.
2. All deps are enabled in this file, even gtest and benchmark which aren't necessarily required.
3. Windows build of gtest fails because it needs MSVC 19.44, while the runners have 19.14 because we had to downgrade them.

[trisyoungs]

Superseded by #2237.