* Remove context (enclosing type name) from C# parser.
* Add a test demonstrating that unicode escapes are significant to determining if a method is a ctor.
This is a prerequisite to #367

* Use DSRN version 1.7.0-beta-25631

* Fill in missing document entries in PDB tests

* Update pdb to xml converter to 1.1.0-beta1-62106-02

* Full Windows PDB determinism

* Update DSRN to 1.7.0-private-25621

* Avoid caching zero chunks

* PR feedback

* Load DSRN from alternate path if set

* Fix error reporting

CompilerPackage was previously being lazy and would just delete and
rewrite files as needed when the package was loaded, even if the
machine would ultimately be left in the same state at the end.
For the old project system (which didn't monitor such file changes)
this wasn't bad, but with the new project system it now reloads projects
in response to changes which can be quite expensive.

Fixes dotnet/roslyn#21838.

https://github.com/dotnet/sdk/issues/1552

These projects reference the compiler EXE projects and hence copy them
to the output directory. This appears to not cause the correct
app.config file (ex csc.exe.config) to be copied along with it. It's
missing the necessary binding redirects that are generated from a direct
compile of the project. As a result when it' invoked from the unit tests
it fails.

It's possible this is a SDK bug and I will dig into that. For now though
I need to unblock the suites.

This changes the unix legs to use the 2.0 SDK. They are likely to suffer from the
same problem as the windows CoreClr leg in that they aren't producing XML files. But
we should be able to fix both of those at the same time.

This is at least temporarily using `dotnet vstest` to execute the tests.
That allows us to run the tests but can't do things like generate
compatible XML files that Jenkins can process.

The new structure of the tests does mean that our Linux / Mac jobs are
now broken though since we no longer have the deploy project.

This primarily moves us to the 2.2.0 version of xunit. In order to make
that transition though a number of other changes needed to happen as
well:

1. Needed to move our desktop target to 4.6.1. This should've been
required some time ago but we were essentially depending on bugs in the
SDK / NuGet.
1. Remove the DeployCoreClrTestRuntime project. This entire idea
depended on having the xunit.console.netcore package. This has since
been deleted and doesn't work with the 2.0 SDK.
1. Remove the deploy compiler tools project. Can just use dotnet exec
now and that's much more efficient.
1. Resolve a new ambiguity with KeyValuePair. A helper of ours now
exists in netcoreapp2.0.

I fully expect a number of Jenkins legs to fail with this change: build
correctness, coreclr and ubuntu. But I want to validate our other legs
and am still trackind down answers needed to fix the others.