Move to Central Package Management

[nytian]

This PR moves to Central Package Management

• Add Directory.package.props for CPM.

• Remove all versions at each csproj

[sebastianburckhardt]

I am seeing a lot of warnings in the build output, like:
Found conflicts between different versions of "Microsoft.Bcl.AsyncInterfaces" that could not be resolved.
Is this related to the package management?

[sebastianburckhardt]

The samples were designed to use the published package, not the locally built one. I suppose you are changing this so it works with centralized package management?

I am not sure what the reason was to use the published package. Probably so that the sample runs standalone and users can copy/paste it easily. That will of course no longer work with the centralized package management. But it's probably not a big issue.

[nytian]

I can switch it back definitely. I thought we should make samples built on the latest Netherite and thus use the locally built one.

[sebastianburckhardt]

Left some comments, otherwise LGTM.