copy_local: true has no effect on netstandard projects

Description

Dependencies are not copied to the output directory of a project targeting netstandard2.x (but they are for net4x).

Repro steps

Please provide the steps required to reproduce the problem

1. dotnet new -i "MiniScaffold::*"

2. dotnet new mini-scaffold

3. After restore/build completes, check {proj}\bin\Debug\net461 and see dependencies copied. Check {proj}\bin\Debug\netstandard2.1 and see no dependencies copied.

If possible then please create a git repository with a repro sample or attach a zip to the issue.

Expected behavior

Expect copy local behavior to match paket directive. This is rather important for building certain things, like type providers. I also think this is the root cause of BenchmarkDotNet#1392.

Actual behavior

The paket directive seems to not matter. See also: #3645, #3352, #3154, #3186.

Known workarounds

None? Using PackageReference instead of paket, I guess

Start with the MiniScaffold reproduction and compare the built net461 and netstandard2.1 output directories after restore/build. Review the copy_local behavior and the related issues #3645, #3352, #3154, and #3186; done means dependencies are copied for netstandard2.x as they are for net4x.