Adds fallback folder for full framework and multi-tfm projects.

[livarcocc]

Customer scenario

Fallback folders were not being set for full framework projects nor multi-tfm projects. Adds fallback folder for full framework projects by removing the condition on the project being netstandard or netcore. Also, sets the properties for multi-tfm projects. We did that by evaluating all the TFMs in the project and if any of them target a 1.x project, we default to PackageSource, as we need to use the lowest common denominator here, so that the project will work independently of the TFM.

Bugs this fixes:

Fixes #1389

Workarounds, if any

Don't use the offline cache. Instead, we will hit the web during restore for Multi-tfm projects.

Risk

Low

Performance impact

Low. We are running another set of inner-loop evaluations.

Is this a regression from a previous update?

Yes.

Root cause analysis:

We were only setting the property for NuGet in the inner-loop.

How was the bug found?

Partner team.

@dotnet/dotnet-cli for review

@MattGertz for approval

[livarcocc]

@emgarten

[emgarten]

This looks good to me, Restore should read the properties after this target runs.

[livarcocc]

@emgarten does restore in va use the same target?

[emgarten]

VS restore is nominated from the project system, it wouldn't be the same.

@natidea is there a target that runs before restore properties are checked? Does CollectPackageReferences run first?

[livarcocc]

We use _GenerateRestoreProjectSpec in another target, should we use the same here? We want the SDK NuGet properties to be set for both CLI and VS.

[livarcocc]

@emgarten _GenerateRestoreProjectSpec does not work, I just tried it.

[emgarten]

_GenerateRestoreProjectSpec would be called later than _GetRestoreSettings

[natidea]

The nomination in VS runs after the Design Time build completes and all targets have run. So yes, CollectPackageReferences is always run before hand, unless the DT build fails before the target has run.

[nguerrera]

@natidea Aren't all design-time builds done on the inner/configured project?

[livarcocc]

Closing this for now. Will re-activate when we have a solution that also works in VS.