Avoid race conditions when building linker tests

[ViktorHofer]

Fixes #40398
Depends on dotnet/arcade#6936

Changes:

• Use static graph restore for linker tests
• Use in-proc MSBuild task to publish linker test projects
• Enabled parallel building of linker tests
• Code clean up...

Filed #48027 to fix an unnecessary excessive amount of NuGet invocation.

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Issue Details

---

Fixes #40398

Changes:

• Use static graph restore for linker tests
• Use in-proc MSBuild task to publish linker test projects
• Enabled parallel building of linker tests
• Code clean up...

Filed #48027 to fix an unnecessary excessive amount of NuGet invocation.

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

[joperezr]

@ViktorHofer are we waiting for the linker version PR to get merged on Arcade first in order to merge this? If this is not currently blocked, it would be good to get it in since I'm currently working on adding a browser-wasm leg for the trimming tests, and it will be much easier to do it once we publish the test apps in-proc in order to be able to import all of the current infra for building the wasm bundle.

[ViktorHofer]

To make sure that the right linker is always used we require a newer SDK as ILLink imports were wrongly sequenced. That said, the right linker is currently used and I don't think we should block the PR on that. Just need an approval and then it's ready to be merged.

[eerhardt]

This looks reasonable to me. Thanks for helping out here, @ViktorHofer!

[ViktorHofer]

The build hang for 2h during downloading CoreCLR artifacts. Pinged @MattGal about this offline.