In the case the CLI was previously downloaded but not yet on `%PATH%` we
need to manually add it there. Not doing it leads to cases where MSBuild
can't find the proper SDK and as a result failing the build.

closes #25649

There is now just a `-build` option. The `-buildAll` option was
introduced at the time when our official and normal build had fairly
significant differences. Now the delta is very small. Removing this as
it's no longer relevant.

DevDivInsertionFiles.vbproj is the last project which isn't included in
Roslyn.sln. Included it there and remove the solution that used to drive
it's build.

This change moves the captured xunit standard output file into the
standard log folder.

closes #25602

This moves all of our build diagnistic output into the same folder:
Binaries\Configuration\Logs. Having it in a single folder is necessary
for us to upload the information using the VSTS Build Artifact task.

Jenkins should be unaffected. It supports and uses wildcards for the
file types we need to be uploaded on failed builds.

This moves Roslyn to use the 2.1 SDK.

This may appear to be moving the SDK version backwards from 2.2 to 2.1.
In reality though it is a move forward. There was a brief time when the
SDK switched their versions to 2.2 before reverting back to 2.1. Roslyn
took a dependency on SDK in that small window.

More details available here:

https://github.com/dotnet/announcements/issues/57

Changes our task to multi-target between net46 and netcoreapp2.0. This
matches how the rest of the SDK is deploying and makes for a smoother
integration into CLI.

context #24646

We need xml files to report results to MicroBuild. This is what our
build queue expects but must have been broken semi-recently.

Previously we were using xunit.console for desktop tests and dotnet-xunit for our
CoreClr tests. This change unifies us on top of xunit.console (now that it has a
netcoreapp2.0 version available).

This PR fixes the CoreCLR compiler server on Windows and changes our bootstrap 
build to act as a test case. The build was previously failing during pipe ownership verification
because the required API was not available through reflection. This change
uses the System.IO.Pipes.AccessControl API to do pipe ownership verification
instead. However, System.IO.Pipes.AccessControl is operating system dependent 
and thus ends up in the runtimes subdirectory next to the build task.
Unfortunately, there is no mechanism for automatic assembly resolution
of plugin DLLs like MSBuild tasks, so we have to implement something
similar ourselves. This change hooks assembly resolution and, when we
see a well-known DLL request, we redirect it to the appropriate path.

Fixes #20900 and #24072

Can now specify "-binaryLog" to Build.cmd and it will produce a binary
log for every invocation of MSBuild. The logs will be written out to the
`Binaries\Logs` directory.

The dotnet pack command can't handle nuspec files (or at least I can't
find the appropriate documentation for it). As such contining to use it
for creating NuGet packages for now.

These were moved in https://github.com/dotnet/roslyn-sdk/pull/21

Need to wrap the property group in the test Directory.Build.props file
with a PropertyGroup.

VS should be inheritting the %TEMP% value we are setting. On the off
chance it gets the original value though lets copy the props / targets
files there to see if this is the cause of the hang.

The repository is fully converted over to the new SDK but there were
still a few remaining references to the classic SDK in the central build
targets. Removing them now that they are no longer needed.

These projects are no longer needed. Removing them.

Historically these were used to create an uber VSIX that nested all of
our other VSIX for a single deployment point. In practice though we have
not actually used these. The install / uninstall issues around them are
too problematic.

Should the uninstall issues be fixed we will consider bringing these
back