Consolidate packages.config restore implementations by minimizing discrepancies

[nkolev92]

Unfortunately we have 3 different implementations of packages.config restore.
A lot of that is due to the difference in reading the packages and part of it is not wanting to make public APIs for PC restore.

Those 3 implementations are:

nuget.exe restore
msbuild.exe /t:restore
VS restore
There's a bunch of differences in how the PackageRestoreManager gets called. It's made my work for PC restore vulnerability checking challenging, because the calls are not unified.

[ghost]

@nkolev92 Issue is missing Type label, remember to add a Type label