CSharpAnalyzers.Vsix.vbproj was pulling CSharp targets and csc.exe, so their supressed warnings were not being respected.
Suppressed this warning in CSharpAnalyzers.Vsix.csproj.

This reverts commit 662593ba.

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

These characters cause problems with MEF with how they make directory paths.
The bug in MEF will get fixed in Dev15.  However, in the meantime, this gives
us a workaround so that we stop getting mef corruption errors.

Ensured that all uses of app.config in our product / test code base is
used in the lower case form.  This helps with our Unix efforts where
mixing the case can be significant.  Updated all of the project
references to ensure they used the lower case version as well.

This fixes #2127

This change disables AppDomain isolation in the unit tests that don't require it.  This is necessary for our goal of running many of the suites on CoreCLR and helps reduce our exposure to #6358.

The AppDomain creation code incorrectly used AppDomain.CurrentDomain.BaseDirectory as the new base directory.  There is no gurantee this points to the directory containing the unit test binaries and this is actually the case in xunit without AppDomains.  Instead it points to the directory containing xunit.oconsole.x86 and uses AppDomain.ResolveAssembly / LoadFrom to resolve unit test binaries.

Switching over to no AppDomains in xunit was causing the creation of RuntimeAssemblyManager across AppDomains to fail.  The error given was a failure to load Roslyn.Test.Utilities.Desktop in the original AppDomain.  This is odd given that the code is executing inside Roslyn.Test.Utilities.Desktop.  The error was fixed by hooking AppDomain.AssemblyResolve in the original AppDomain and essentially reloading the DLL.  I'm not completely sure why this worked but I suspect it has to do with the original AppDomain having an incorrect base directory.

Updating System.Reflection.Metadata to 1.1.0-alpha-0015 and System.Collections.Immutable to 1.1.37.0

Revert "Updating System.Reflection.Metadata to 1.1.0-alpha-0015 and System.Collections.Immutable to 1.1.37.0"

This reverts commit d78dbb97.

Updating System.Reflection.Metadata to 1.1.0-alpha-0015 and System.Collections.Immutable to 1.1.37.0

Reverting System.Collections.Immutable back to 1.1.36 until we can upgrade System.Reflection.Metadata simultaneously

Updating Microsoft.DiaSymReader to v1.0.6, Microsoft.DiaSymReader.Native to v1.2.0, and System.Collections.Immutable to v1.1.37

* 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)