* 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.

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.

It's contained in the diagnostics window VSIX, which we include in
the full deployment.

Instead using a facade/mixin approach to more cleanly pull this off.

More cleanup to do between RoslynCompletionSet and
FilteredRoslynCompletionSet.

1. Reference a bunch of stuff from Nuget packages instead of VS.
2. Move to Update 2 versions of packages.
3. Now that we are using the packages, we're referencing
   Microsoft.VisualStudio.Shell.14.dll instead of .15 again.  This means
   that types that moved to Shell.Immutable.15 are not type forwarders.
   Luckily we didn't need anything from Shell.Immutable.15 in the project
   where it was a problem.

Extending the supported functionality of the VisualStudio IntegrationTest Utilities and adding the start of 'CSharpAutomaticBraceCompletion'

Samples.sln and Roslyn.sln were fighting over the GUIDs of Immutable, Metadata and Compostion.
Searching across the tree, and made sure that they were the uniform everywhere to prevent this.

This brought along some references to Microsoft.VisualStudio.Threading
that we previously didn't have. Nothing was wrong with this, but it
meant I had to fix some namespace qualifications that were assuming the
"Threading" namespace was unambiguous.

To prevent projects across the tree from having different dependencies, we unify
external package dependencies by creating empty C# projects that represent them.
We then make use of project.json package inheritance (where a project inherits
all packages dependencies from their dependencies) to unify it across the tree.

No projects outside of this tree, should be directly referencing versions of
these dependencies manually.

For this check-in I've tackled Metadata, Reflection, and DiaSymReader. Will tackle
the rest in future commits.

Also add support for completion item filtering.

This is the implementation assembly with implementation details that
we should not depend upon from our shipping binaries.

PIAs always have the version of the Visual Studio they shipped with,
even in higher versions of Visual Studio. We should reference the fixed
version that matches the PIA.

We use some public types from assemblies that aren't in the SDK. We
previously picked those up from the GAC but there's no guarantee that
they are there.

Initial work to add support for external language service result providers for Find All References, GotoDefinition and NavigateTo.

All the newly added result provider interfaces are internal, and would eventually go through API design review to enable third party plugin implementations.

We already grant internals access from higher and lower layers, so
this is nothing surprising.