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

* Merge pull request #12041 from heejaechang/buildsyncrace

found one more case where documentId can be null

* prevent VS from crashing if VS got shutdown while build error reporting is in progress.

* Update our NuGet package version to 1.3.2

* Update Microsoft.DiaSymReader.Native to 1.4.0 RTM (#12141)

* Enable building of release nuget packages.

This commit makes it so that we will always try to generate release nugets except if they depend on prerelease packages. If one of our nuget packages happens to depend on prerelease packages, then when building release nugets, we will simply print a message in the build output and skip release nuget generation for that package (and allow the overall build to succeed).

* Address code review feedback.

* Simplify script to use nuget.exe for prerelease dependency validation instead of adding custom logic in the script for this.

* Remove Microsoft.CodeAnalysis.EditorFeatures from list of prerelease nuget packages.

* Change the name of the error log file to skipped_packages.txt.

* fixed DifferenceViewer leak

this leak was responsible for about 14% of managed memory in customer's dump.

basically, in certain condition, if cancellation exception is thrown, we will not close difference viewer which cause
all text views to leak. that cause all taggers and text buffers to leak and that cause our preview workspaces to alive.
which in turn cause all solutions to alive and so on. all those objects (view, buffer, workspace, solution) are quite
big graphs. so ends up eat up 14% of memory.

added assert to make sure if we leak viewers again, we get some kind of notification.

Updating 'GenerateCompilerExecutableBindingRedirects' to produce version numbers with 4 parts.

Move some code into the open

* Merge pull request #12041 from heejaechang/buildsyncrace

found one more case where documentId can be null

* prevent VS from crashing if VS got shutdown while build error reporting is in progress.

* Update our NuGet package version to 1.3.2

* Update Microsoft.DiaSymReader.Native to 1.4.0 RTM (#12141)

* Enable building of release nuget packages.

This commit makes it so that we will always try to generate release nugets except if they depend on prerelease packages. If one of our nuget packages happens to depend on prerelease packages, then when building release nugets, we will simply print a message in the build output and skip release nuget generation for that package (and allow the overall build to succeed).

* Address code review feedback.

* Simplify script to use nuget.exe for prerelease dependency validation instead of adding custom logic in the script for this.

* Remove Microsoft.CodeAnalysis.EditorFeatures from list of prerelease nuget packages.

* Change the name of the error log file to skipped_packages.txt.

* fixed DifferenceViewer leak

this leak was responsible for about 14% of managed memory in customer's dump.

basically, in certain condition, if cancellation exception is thrown, we will not close difference viewer which cause
all text views to leak. that cause all taggers and text buffers to leak and that cause our preview workspaces to alive.
which in turn cause all solutions to alive and so on. all those objects (view, buffer, workspace, solution) are quite
big graphs. so ends up eat up 14% of memory.

added assert to make sure if we leak viewers again, we get some kind of notification.

Move NuGet.exe restore location back to the root

After extensive testing it appears the number of places that assume NuGet.exe is in the root is "at least one more."  Need to unblock the signed build so putting it back in the root temporarily.

Download NuGet.exe instead of having it checked in

Add a /clean option to Restore.cmd

Move SourceGenerator to a feature branch

When present this option will clean out all of the NuGet caches before doing a restore.

This is necessary to remove our hard coded dependencies on NuGet.exe in our official builds.  Once they are removed we can switch to dowloading NuGet.exe on demand vs. checking it into the repo.

Skipping the InteractiveWindow Clipboard UnitTests as they cannot run on VS2015.2

Ensure the right binder is used to bind initializer of implicitly typed variable.

Add some unit-tests.

Fixes #12266.

Related to #9021, #12078, #12266, #12267.

Expand condition on our command line generator Tasks

Add check for empty/no change

Expanded the Condition check to verify the input file is non-empty.  Lacking this we get the following spurious entries in our MSBuild output files:

```
GenerateSyntaxModel:
Skipping target "GenerateSyntaxModel" because it has no outputs.
``

Adding the condition removes this entry and makes our build log files just a bit more readable.

Report errors and exceptions from source generators

Updating the InteractiveWindow ClipboardTests to match the expected clipboard format in Update 3.