Use PackageReference for C++ dependencies

[JunielKatarn]

See dotnet/project-system#2491 (comment)

MSBuild AND Visual Studio now support PackageReference dependencies for MSVC projects.
Using this will significantly reduce the project file clutter and largely simplify dependency management introducing the following enhancements:

• Consolidate NuGet dependency declaration into the VCXPROJ file (drops packages.config.
• Allows importing nugets directly from the GlobalPackagesFolder instead of creating local copies per repository clone, saving a fair amount of disk space (drops packages folder).
• Aligns with the .NET restoring style (msbuild /t:restore).
  Bonus:
• Allows to easily parameterize/interpolate package names and versions, as package references are merely MSBuild Item declarations.

Note, this change should be transparent while using Visual Studio but the MSBuild CLI and the CI restore steps will be affected.

Before:

NuGet.exe restore <solution>
MSBuild <solution>

After:

MSBuild /Restore <solution>

Pre-merge checklist

• App and lib templates for C++ should be using PackageReference too (under discussion).
• The CLI should be updated to deal with PackageReference.
  • Revise the logic in auto-linking which updates packages.config.
• Make sure we bring in WinUI 2.x
  @asklar: (i see it's commented out now), and that opting into winui3 brings it in
• Validate that apps can continue to override the WinUI 2 version by updating ExperimentalFeatures.props.
• Validate creating new app and auto-linking works properly.
• Review removal of RestoreLockedMode.
  Use PackageReference for C++ dependencies #8195 (comment)

Future work this PR will allow us to do after merge:

• Leverage packages.props files
• [ ] Remove the /p:RestorePackagesConfig=true once all packages.config files are gone.
  Useful for mixed PackageReference/packages.config projects when combined with RestoreProjectStyle=PackagesConfig.
• Update website documentation to advertise this change to RNW users.
• Clean up CI from redundant NuGet Restore workflows.
• Consolidate most relevant package names and versions into shared props files.

Microsoft Reviewers: Open in CodeFlow

[NickGerleman]

Love the overall change.

@JunielKatarn do you know the min version of VS this requires? Because end-users are buildings our source in addition to CI, there's some different versions out in the wild we need to support.

@asklar maintains some scripts and documentation for this that may need to be updated, if the min required version goes up.

This might require those manually doing a NuGet restore to change their logic, so I'm going to label this as breaking so a callout can be added to release notes?

[asklar]

Love the overall change.

@JunielKatarn Julio Cesar Rocha FTE do you know the min version of VS this requires? Because end-users are buildings our source in addition to CI, there's some different versions out in the wild we need to support.

@asklar Alexander Sklar FTE maintains some scripts and documentation for this that may need to be updated, if the min required version goes up.

This might require those manually doing a NuGet restore to change their logic, so I'm going to label this as breaking so a callout can be added to release notes?

from a functionality standpoint this should be transparent to users - if they need to run something differently, that'd be a problem. If they are using the CLI or VS, this should just work

[JunielKatarn]

Love the overall change.

@JunielKatarn do you know the min version of VS this requires? Because end-users are buildings our source in addition to CI, there's some different versions out in the wild we need to support.

@asklar maintains some scripts and documentation for this that may need to be updated, if the min required version goes up.

This might require those manually doing a NuGet restore to change their logic, so I'm going to label this as breaking so a callout can be added to release notes?

If I recall correctly, it is Visual Studio 16.9.
But MSBuild has had this capability for a while, according to @wjk (can you please confirm)?

[NickGerleman]

Chatted offline with Julio about the change. E.g. what would be good to validate.

We have manual + UT validation for autolinking looking good. As part of this change, Julio will add a document to our website to guide users on any migration they may need to do. run-windows will continue to restore NuGet packages for community modules using packages.config out of the box.