Add test for specified behavior of a virtual method invocation (via a binary compatibility scenario). (#16055)

* Add test for specified behavior of a virtual method invocation (via a binary compatibility scenario).

Format the coalesce expression we produce.

Fixes #16025

Enforce DocumentationFile is a centrally controlled property

This property is controlled by our central build targets.  It shouldn't be used in indivdidual projects anymore as it can lead to bugs.  See the following PR from @KirillOsenkov for an example of how this leads to bugs

https://github.com/dotnet/roslyn/pull/15880

Remove EmitContext from ITypeReference.TypeCode

Fix ability to run portable tests with TDD, F5, etc ... 

Combine duplicate methods

Fix XML doc name for BasicInteractiveEditorFeatures

Cleaning up the open integration framework

Fixes #15734

Fixes #15934

Fix the ThrowingTraceListener on portable unit test runs

At this moment there is no supported way of building a portable DLL and deploying
current OS dependencies (say windows) as a default.  As a result these DLLs are
not full deployed post build (not runnable) and this breaks any number of
tools developers use to be productive: F5, TDD, WPF xunit runner.

Roslyn works around this for official builds by using deployment projects.  This
is a project per supported delpoyment (Desktop, CoreCLR) which consists of a
dummy EXE and referenes all of our portable DLLs.  Hence they DLLs as they exist
in that output directory are fully deployed.

This makes it possible to do official testing with confidence but doesn't developers
who want a more rapid feedback experience.

This change makes it possible to do direct testing again by adding an ad-hoc deployment
mechanism.  This uses the same code as the official deployments but is still ad-hoc
so it won't be used for official builds: just developer builds.

Here is the bug on MSBuild tracking the real bug and fix

https://github.com/Microsoft/msbuild/issues/1499

* moving naming styles types into the workspace layer.
Teaching abstract options serialization service about naming styles.

* Implementing naming styles support for editorconfig

* responding to david's PR feedback

* responding to Jason's feedback

* responding to Jason's feedback part 2

* addressing the latest set of comments from David

* addressing Jason's comments

* addressing Kevin's comments

revert expected vssdk wizard version

Fix crash when "fix all in solution" is used with "inline declaration".

Fixes #15994

Revert "Update versions in post-dev15 branch to 2.1.0-beta1"

This reverts commit 436dd2c0.

We want master to remain version 2.0

Unify error messages on extension methods omitted type arguments

Misc build fixes

For cases where git isn't on the path, git is an older version that
doesn't support all the flags we need or the repository we are building
is not actually a git repository.

- Sending telemetry isn't really interesting for the CI build.
- Restoring a local package cache also isn't useful.

- Use `dotnet-install.sh` to get the CLI instead constructing download
  URLs by hand.

- Use a newer version of the CLI when building (this is the same version
  that CoreFX and CoreCLR use).

- Change how BaseNuGetRuntimeIdentifier is computed when running
  on *NIX. We now use the information from /etc/os-release (which is
  what the CLI does internally).

With these changes, I've been able to build Roslyn on RHEL by updating
the runtimes sections of the relevent project.jsons to include
"rhel.7.2-x64".

For the set of assemblies we build on *NIX, we should also be able to
build the coresponding nupkgs so they can be used by other repositories.

On *NIX we have a case sensitive file system, so we need the correct
casing in the .nuspecs.

We should build this tools when we are doing the cross platform build,
they are useful to have as part of the build output.

In the general case, finding the correct crossgen to invoke is non
trivial since there's no strong corespondence between the host Runtime
ID (which is easy to compute) and the RID that crossgen would be
packaged in.

For example both RHEL and Centos have crossgen packaged in a nuget
packages that uses `rhel.7-x64` as the RID, in order to share the
package across minor versions of RHEL and Centos (which is binary
compatibile).

Since we can build Roslyn without crossgening the bootstrapped
toolchain, I'm exposing an option to allow skipping of crossgen for
platforms where a developer knows apriori that `crossgen.sh` would not
compute the correct RID and fail.

This fixes a MSB3568 warning during the build of CrossPlatform.sln on
Linux.

Add csi.exe.config to compilers vsix

Add csc and vbc to PATH

See #15751