Gets us better data on what is actually taking time on the runs.

The Jenkins build is copying Newtonsoft.Json into the output directory.  This is not happening locally and the version chosen by Jenkins is not compatible with the one we are referencing here.  Moving to own output directory to eliminate this issue.

In preparation for moving to web storage.

This reverts commit 57a34148.

This reverts commit 760e1204.

This reduces package restore on Roslyn.sln with all packages already restored from 40 seconds -> 10 seconds.

project.lock.json format has changed since we last updated.

The test caching layer had two bugs around re-hydrating the test resutls from cache:

- Made a bad assumption about the name of the file.
- Assumed tests were always rehydrated into the original directory.

closes #8860

This reverts commit e2fc5135.

This reverts commit e3c1ea08.

This reverts commit 8f26ffb5.

This reverts commit 662593ba.

This still only runs the tests on desktop (for now), but it makes
it possible to run them on coreclr.

Synchronize all corefx references to -23504 and bring in the
xunit coreclr test runner.

The script for creating / uploading the NuGet file was failing to include the .nuget directory in the ZIP file.  That caused everything to be unpacked to ~\packages instead of ~\.nuget\packages.

The previous PR worked because the new packages weren't being actively used in the master branch (consumed in a child branch that's a WIP).  This PR corrects the issue in the upload scripts and re-generated the ZIP.