VSL is a name no longer relevant to Roslyn.  Begining it's removal.

This change needs to be comitted first so I can clean up some internal code.

TLDR: artifacts are going to move around in Binaries\Debug and the directory is going to get a lot bigger.

At a high level build projects can be classified into three categories based on how they write output:

- incorrect: a given output path is written to more than once with different contents
- less correct: a given output path is written to more than once but always with the same content
- correct: a given output path is written to exactly once

Today the roslyn build is decidedly “incorrect” as pretty much every file is written directly into Binaries\Debug. This means it ends up writing pretty much every Visual Studio SDK DLL twice: once for Dev14 and once for Dev15. For example at various points in the build Binaries\Debug\Microsoft.VisualStudio.Text.Data.dll may refer to Dev14 and at others it’s Dev15. If this seems like a scary proposition for a build that’s because it is indeed scary and it has real consequences. By now pretty much everyone on the team has hit the build race condition that is dragging down our PRs.

The general fix here is to move build outputs into separate directories. Instead of building to $(Configuration) projects now build into say $(Configuration)\Exes\$(MSBuildProjectFileName). This will have a substantial increase in the size of Binaries. We will be looking into ways to reduce that. In the short term though build stability far outweighs the size increase.

This change takes us most of the way to "correct". There are several places I had to compromise in order to get this initial change in:

- UnitTests still build to a common output folder (one for Dev14, another for Dev15). Pulling unit tests apart is going to take a bit of work.
- Every project has a <RoslynProjectType> entry. This will go away in the future for most projects. It's temporarily needed so I can fix roslyn-internal in parallel without taking down the build.
- VSL.Imports.targets is messy. Unavoidable for now due to the above. It will get cleaner as I iterate on this.

None of these are relevant to the underlying race condition. Hence it's okay to push them off.

This won't work anymore. The correct check is in VSL.Versions.targets
line 21, which would fire before this anyways.

Binaries in Roslyn have only three possible signing states:

1. Public signed with Microsoft controlled keys (shipping binaries)
2. Real signed with a full key in the Roslyn repo (non-shipping binaries)
3. Not signed

Our build targets still had a lot of dead logic around our old methods which included delay signed binaries.  This cleans all of that up and removes some dead variables.

Ensure IBC is running for our official builds.

There will be a corresponding update to the Build Definitions to provide the $(IbcMergePath) value.

This works around #12458. The warnings are annoying and also break
the project system in slightly bad ways.

Batch sign tool for speeding up our signed build time.

We haven't used this for ages, and is most likely terribly broken.

We're have required Update 2 for some time, making this unnecessary.

This got switched during the MicroBuild merge somehow. This switches
it back.

This refactors our SignVsixInputs task into two pieces, one that
simply computes the list (so we can validate it) and then the other
piece that actually does the signing. The first bit runs always, even
on non-signed builds.

* Move Roslyn to newer toolset packages

1. Move to 1.2.1 compiler toolset package.
2. Move to 1.2.0-beta1 analyzer packages.
3. Turn on IOperation feature flag for all projects as the new analyzer packages have IOperation based analyzers.

* Use the Roslyn wide default CA rulesets for newly added samples project.

* Fix couple of test projects to use the Roslyn wide rulesets for code analysis.

* Move to analyzers 1.2.0-beta2 packages (multiple fixes and enhancements to Roslyn diagnostic analyzers)

* Revert accidental file mode changes.

* Move shipped implicit constructors to public API shipped files.

Fixes #11446

The NuGet packages for the SDK don't currently support cross-targeting,
so we must pick the right version to consume based on the version of
Visual Studio you are targeting. I implement this by simply restoring
both versions, and conditioning our MSBuild includes to the right one.
The annoying bit is since we need to restore two different versions
of the same package name via NuGet, we have to put the dependencies
in separate project.json files.

Fixes #10407.

Replaced usages of these build properties with UseCommonOutputDirectory, which is a built-in concept.

This fixes a signed build failure, we asking reference projects to return the result of
GetTargetPathWithAuthenticodeCertificateName, but this was being called on projects that
never end up in the VSIX. Mimic the same logic that VSIX uses to figure out if goes in the VSIX.