This commit updates the `AnalyzerDependencyChecker` type to reflect the
recent changes to require all analyzers and dependencies to be
specified, and the changes in how we load analyzer assemblies.

Now that we require all analyzers and dependencies to be specified, we
no longer look next to the specified analyzers to optimistically locate
dependencies. Instead, we only consider the list of passed-in analyzers
*plus* the assemblies already loaded into the `AppDomain`. The latter
avoids unhelpful warnings in the event that the analyzer assembly
includes a code fix that take a dependency on a Visual Studio assembly,
which of course can't be included in the list of analyzers. We now
create a warning when we identify a missing dependency.

We now also check analyzers themselves for conflicts (i.e., assemblies
at different paths with the same identity but different contents)
instead of just their dependencies.

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

Right now the IDE uses the Csc/Vbc host objects from the build
task by loading the task from the GAC (since the task is only
installed in the MSBuild directory otherwise). However, this breaks
using a different task for ETA tests since the GAC will always
take precedence.

This change adds the build task to the VS setup to include the
task in the IDE installation.

In C#, if a WinForms InitializeComponent method() includes character
literal containing a unicode escape for a character that is not valid in
XML, it can cause an XML parser exception to be thrown and the WinForms
designer not to load. To work around this problem, we generate a hidden
cast expression in the IMethodXML to cast the numeric value of the
character to a System.Char.  We do this for any character that isn't a
letter or digit. The designer can process this XML correctly and load
properly.

Fixes part of internal TFS bug #1167415.

We have reports of the BufferUndoState being unavailable in
UndoTemporaryEdits when inline rename has been dismissed due to an
external workspace change. This change prevents the crash by checking
for the existence of the relevant BufferUndoState while we await more
information on what leads to this state.

The RoslynPackage type originally lived in a seperate assembly than
Microsoft.VisualStudio.LanguageServices when it was important for us
to be able to support the core parts of Roslyn being installed atop
the existing Visual Studio 2013 language services. This is no longer
a supported scenario anywhere, so we should just get rid of the
assembly.

Doing this is easy, it's just a matter of moving the files and related
assets to the LanguageServices assembly. A MEF interface is added
to prevent a circularity around triggering a load of stuff in the
SolutionExplorerShim. That could be delt with later by moving the core
of that code back to LanguageServices, but I don't want to touch that
now since it's very sensitive.

Assert if we are not on the UI thread and give test authors the choice
to explicitly pass in the default namespace.

Attempting to generate a new file in an ASP.NET 5 web project would
deadlock because we were attempting to get the default namespace from a
worker thread.

The solution is to move the work of computing the default namespace from
ComputeOperationsAsync to GetOptions.  GetOptions is always guaranteed
to execute on the UI thread wheras ComputeOperationsAsync happens from a
worker thread.

This reverts commit 779cea70.

Attempting to generate a new file in an ASP.NET 5 web project would
deadlock because we were attempting to get the default namespace from a
worker thread.

The solution is to move the work of computing the default namespace from
ComputeOperationsAsync to GetOptions.  GetOptions is always guaranteed
to execute on the UI thread wheras ComputeOperationsAsync happens from a
worker thread.

This removes the majority of references to the deprecated Desktop
assemblies.  The only remaining ones are in the VSIX projects.  They
must remain until we actually delete the assemblies.

Fixes internal TFS bug #1128063

When NavigateTo is invoked on an IGraphNavigateToItem from the UI
thread, we are now careful to maintain control of the UI thread to
ensure any existing NewDocumentStateScope is preserved.

Fixes internal bug #1168460.

Fixes #1436

Fixes internal bug #1168460.

Fix #1873 Add support for SetType & AddParameter in Declare Sub and
Function

Fix paths to System.Collections.Immutable and Sysytem.Reflection.Metadata in VisualStudioSetup.csproj

Fixes #1512

The solution explorer context menu that allows users to change severity of analyzer-reported diagnostics currently displays the following entries -
    Error
    Warning
    Info
    Hidden
    None

When the context menu is displayed, a check mark is displayed next to the entry representing the severity of diagnostic as configured in the project's ruleset file. This works fine in cases where a severity is explicitly specified for the diagnostic in the ruleset file.

However, in cases where the severity is not explicitly specified in the ruleset file, the diagnostic is assigned its 'default' severity and we don't display a check mark against any entry in the above menu. As noted in #1512, this is confusing because the 'default' severity is also one of the severities listed above.

This change introduces an additional entry named 'Default' in the above menu that will be checked in cases where the dagnostic does not have an explicitly specified severity in the ruleset file. If the user clicks this entry to change the severity of some diagnostic to 'Default', the entry corresponding to this diagnostic is removed from the ruleset file.

Update `AnalyzerFileReference` to take an `IAnalyzerAssemblyLoader`
instead of a `Func<string, Assembly>`.