This adds support for a new ICompilerOptionsHostObject which is how we
can pass options through the project system without having to manually
add separate properties for everything as we've traditionally done in
the past. To ensure compatibility with "new" compiler tasks against
"old" project systems, and "new" project systems against "old" tasks, we
continue to use the historical ICscHostObject* and IVbcHostObject*
properties for all existing values, and only use this property to
shuttle through new values. For the rest of Visual Studio 2015, we can
just use this for any new "simple" switches that we must pass along.  We
still would need to do additional work in the project system for any
inputs that are lists of files because of the fast-up-to-date check.

Longer term, there is still the unanswered question of how we want to
future versions of Visual Studio to get command line options to
completely get rid of all language service knowledge of this. There are
two possible approaches:

1. We just use the support added in #4604 and just delete this entirely.

2. We continue to use ICompilerOptionsHostObject. My proposal for that
   would be we continue to use the model of "we pass all options not
   supported by a strongly typed host object interface to
   ICompilerOptionsHostObject", and the project
   system would just remove all support for everything else and
   fail those QueryInterface calls.

This is therefore written with the idea that we could switch to option 2
in a coordinated way, if we wanted to do so.

Fixes #7812, assuming you have an updated csproj.dll and msvbprj.dll
which understands the new ICompilerOptionsHostObject.

Moves the build task code to a shared project that we use to build
at net45 and a portable50 CodeAnalysis MSBuild task. Also upgrades to
nuget v3.2.1-rc since this is necessary to understand the dotnet4.3 spec
used in the project.json.

Simplify the client build by moving to a root type with a desktop and
portable variation.  This allows us to share more infrastructure between
the layers.

Fix a couple of issues:

- Use nameof where appropriate
- Accessibility should come before override

We decided that the current design of this feature would not add much to
the user experience, so we're backing out the parts that have been
committed already. Nothing is using these pieces, so this should even
impact any tests.

Some of the build task names where still set to their old values from
when they were in MSBuild. This changes the names to the proper names
and also ports any missing resources to the resource files in the current
build task assembly.

This commit updates the Vbc and Csc build tasks (and related targets
files) to consume AnalyzerDependency items. They are passed to the
command-line compilers using the "/analyzerdependency" switch, or on to
a build host through a new IAnalyzerDependencyHostObject COM interface.

Brings back the managed client and reworks the two new build
task specific tests to compile using the managed client inside
the build task.

This change brings back the SimpleMSBuild test, which sets
up a "hello world" C#+VB solution and builds it using msbuild using
the build task.

Two build-task-specific tests have also been added, which directly
load and call execute on the Csc and Vbc tasks.

Closes #866.

Been almost a month since the code formatter was run so this change was
a bit larger than would be expected for a normal (weekly) update.  Diffs
mostly around:

- Whitespace changes
- Missing copyright headers
- Missing visibility modifiers

This moves the existing tasks into the source repository for Roslyn, as Roslyn
owns the C# and VB MSBuild tasks.