TLDR: artifacts are going to move around in Binaries\Debug and the directory is going to get a lot bigger.

At a high level build projects can be classified into three categories based on how they write output:

- incorrect: a given output path is written to more than once with different contents
- less correct: a given output path is written to more than once but always with the same content
- correct: a given output path is written to exactly once

Today the roslyn build is decidedly “incorrect” as pretty much every file is written directly into Binaries\Debug. This means it ends up writing pretty much every Visual Studio SDK DLL twice: once for Dev14 and once for Dev15. For example at various points in the build Binaries\Debug\Microsoft.VisualStudio.Text.Data.dll may refer to Dev14 and at others it’s Dev15. If this seems like a scary proposition for a build that’s because it is indeed scary and it has real consequences. By now pretty much everyone on the team has hit the build race condition that is dragging down our PRs.

The general fix here is to move build outputs into separate directories. Instead of building to $(Configuration) projects now build into say $(Configuration)\Exes\$(MSBuildProjectFileName). This will have a substantial increase in the size of Binaries. We will be looking into ways to reduce that. In the short term though build stability far outweighs the size increase.

This change takes us most of the way to "correct". There are several places I had to compromise in order to get this initial change in:

- UnitTests still build to a common output folder (one for Dev14, another for Dev15). Pulling unit tests apart is going to take a bit of work.
- Every project has a <RoslynProjectType> entry. This will go away in the future for most projects. It's temporarily needed so I can fix roslyn-internal in parallel without taking down the build.
- VSL.Imports.targets is messy. Unavoidable for now due to the above. It will get cleaner as I iterate on this.

None of these are relevant to the underlying race condition. Hence it's okay to push them off.

The ImportGroup element is just noise.  It was also used very inconsistently in the repo and often within the same project file.  Just remove it.

The dependency projects serve a few purposes:

- Help ensure package unity by serving as a single place for a NuGet reference.
- Make NuGet updates simple by having a single place to change.
- Grouping together related packages to make it easy to take a dependency on say Visual Studio editor.

The first two points are largely obsolete now that our project.json references are strictly validated on every build and have a single update mechanism.  This meant a lot of our depnedency projects were just making Roslyn.sln bigger.

As such I went through and deleted all of them which had only 1 or 2 project.json entries.  I left the VS ones which tend to group 10+ references together.  They are still serving a valid "reference VS" purpose.

This reverts commit 31377ce7.

Update TargetFrameworkVersions.

To prevent projects across the tree from having different dependencies, we unify
external package dependencies by creating empty C# projects that represent them.
We then make use of project.json package inheritance (where a project inherits
all packages dependencies from their dependencies) to unify it across the tree.

No projects outside of this tree, should be directly referencing versions of
these dependencies manually.

For this check-in I've tackled Metadata, Reflection, and DiaSymReader. Will tackle
the rest in future commits.

This reverts commit d43d4780.

This reverts commit d43d4780.

This reverts commit 7bb0b4ea.

Adding a unit test to validate the PortablePdb Reader/Writer works appropriately with VB DateTime constants

This reverts commit d43d4780.

Since #f9b4d71a, tests inherit app.config if they don't specify one. Removed the ones that match the default behavior.

by removing `<DebugType>` lines from projects that import `VSL.Settings.targets`

We don't need SolutionDir or RestorePackages, which were for very old-
style restore systems.

The casing of app.config was incorrect in several of the project files.
This broke tests on Linux / Mac.  Corrected the case.

* This updates all references to nuget.exe to use the copy in the root.
* This deletes all NuGet.config and NuGet.exe files that are not in the root.
* This removes all references to NuGet.targets (which is obsolete and no longer exists)

The native compiler handled corrupted default parameter values by
substituting in default(T).  It's unclear if this was intentional
behavior in the compiler or not.

Either way though obfuscators took advantage of this behavior and at
least one prominent one will corrupt default parameter values when the
value is null.  Enough prominent libraries have shipped using such
obfuscators that it is a blocker to upgrading.  Hence we need to emulate
the native compiler behavior here.

This change is a bit large because I needed to update the test resources
with a corrupted DLL in order to test out the changes.

closes #4196

Move TestUtilities.csproj and TestUtilities.FX45.csproj to separate directories to accomodate current nuget limitations

This updates the referenced version of 'Microsoft.CodeAnalysis.Test.Resources.Proprietary' from nuget 20150716.7 (20150716.5 and 20150716.6 are also broken) to 20150717.8, which contains the actually signed binary.

Nuget package
Roslyn sources depend on
Microsoft.CodeAnalysis.Test.Resources.Proprietary.1.1.0-beta1-20150716-05
which was not signed, so running tests was broken. I've uploaded a newer
package `07` to nuget.org that fixes the problem. This PR updates the
package references in Roslyn source to consume and build using the newer
package.