Use ProjectReferences for inbox libraries source projects

[ViktorHofer]

Currently inbox source projects use <Reference /> items instead of <ProjectReference /> items. That design dates back to .NET Core 2.0 days, when dependencies were represented differently. With the continuous work over the last years bringing us closer to the customer path, we should consider updating these to use P2Ps instead.

Here are just some advantages:

• Dependencies are incrementally built
• Inbox projects can be built from a fresh clone without any up-front work (!)
• Faster root builds as a separate reference source projects build isn't necessary anymore.

Blocked on NuGet/NuGet.Client#5452

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Issue Details

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Currently inbox source projects use <Reference /> items instead of <ProjectReference /> items. That design dates back to .NET Core 2.0 days, when dependencies were represented differently. With the continuous work over the last years bringing us closer to the customer path, we should consider updating these to use P2Ps instead.

Here are just some advantages:

• Dependencies are incrementally built
• Inbox projects can be built from a fresh clone without any up-front work (!)
• Faster root builds as a separate reference source projects build isn't necessary anymore.

Blocked on NuGet/NuGet.Client#5452

Author:	ViktorHofer
Assignees:	-
Labels:	area-Infrastructure-libraries
Milestone:	-