It's contained in the diagnostics window VSIX, which we include in
the full deployment.

This reverts commit 31377ce7.

Update TargetFrameworkVersions.

Object Browser was forcing compilations to be realized just to compute the assembly identity for each of a compilation's metadata references. With this change, the Object Browser will use the metadata references from the project and call the same utility function that is used to read assembly identity for analyzer assemblies.

Move the files in the compiler that are shared by source with other projects into the Shared folder.  This combined files which weren't in a shared location and those previously in Helpers.

Update 1 defaults to copying implementations for some class libraries, but we
don't need that for our feature binaries.

Adds a new type, CoreClrAnalyzerAssemblyLoader, that is responsible
for finding and loading analyzer assemblies on CoreCLR. This is used
in the CscCore and VbcCore CoreCLR-targeting projects.

Fixes #5267.

* 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* This removes all references to NuGet.targets (which is obsolete and no longer exists)

Cleaning up code. Only scripting uses the TryFindXmlDocumentationFile
helper. So moving it to that project and removing code that it doesn't
need.

The code was duplicated between scripting and workspaces because it is
partially non-portable.  Share the files by linking (and, unfortunately,
ifdef'ing) instead.

This change does two actions to our public API files:

- Resets them to the versions from 1.0.0 RTM
- Splits them into the shipped and unshipped files

"Roslyn" -> "Microsoft" or "Microsoft.CodeAnalysis"

The targets files were previously split into an open version in
Microsoft.CodeAnalysis.Toolset.Open and a closed version in build/. This
unifies the four targets into two new targets, VSL.Settings.targets and
VSL.Imports.targets, and moves all the targets from ..Toolset.Open into
the build/ folder.

These two changes should have been included in
https://github.com/dotnet/roslyn/commit/8c9ed547c5bc6ad5a9842945688da9b2f189ac8c
but,

1. The references didn't match any of the extraneous VSIX names because
they inline variables.
2. OpenSourceDebug.csproj doesn't drop a VSIX in the output folder, so it
was missed by my validation pass.

The net effect is to remove Microsoft.Build.Tasks.Core.dll,
Microsoft.Build.Utilities.Core.dll, and
Microsoft.VisualStudio.Shell.14.0.dll from OpenSourceDebug.vsix.

Mechanically apply <Private>False</Private> to the newly-appeared
references.

This deletes the empty and unused Desktop assemblies from the code base.