Previously, when a VisualStudioWorkspace was constructed we were
doing a bunch of work in the constructor talking to the UI thread. This
was dangerous because we might get composed on a background thread.
This moves the dangerous initialization until we're creating a project
when we know we have a UI thread available.

In this refactoring I moved the project tracker and a few other fields
into a private class so it's more obvious what's dangerous to touch.
I also do a pass through all consumers of the property and either
update it to use the deferred state directly (because we're only
consuming projects, so it's fine if we don't have anything) or to the
factory method if we actually are creating projects.

This does temporarily regress the ability to create projects on
background threads, but it was unclear if that was generally safe to
start with.

This was previously using internal guts of VisualStudioWorkspaceImpl.
Now it's just using honest-to-goodness public APIs.

This was reaching into VisualStudioWorkspace and had methods just to
get things it could have directly gotten from the service provider.

This didn't need anything other than the service provider, so
we can easily decouple that.

Nobody was using this.

C# function breakpoint binding

Publish Assets to dev15-rc2 branch

Don't crash during shutdown if we try creating metadata snapshots

Ensure we don't free metadata from under skeleton assemblies

Package loading time improvements

Remove needless subclassing with refactoring providers.

When we create skeleton assembly references, we back them by temporary
memory out of our ITemporaryStorage service. We used a
ConditionalWeakTable to ensure that if the reference was held alive
that the underlying memory wouldn't disappear. This was subtly
incorrect. If you had a PE symbol from such a compilation, the
compilation is not held alive, and the metadata reference could be freed
but the metadata (which is held by the symbol) could still be held.
This meant we'd free the memory too early and crash.

The fix is simple: root the memory by the metadata object, not the
metadata reference.

Fixes #13243.

Merge microupdate into master

Do not crash on cancellation in FindReferences.
Fixes #15113

The definite assignment errors were fixed by changing the design of local functions
to allow forward calls to local functions in scope.

Fixes #13029

Fix NuGet.exe caching

Don't generate a variable if it would conflict with another local in scope.

Fixes #11777

Make FindReferences work in auto-property intializers.

Fixes #10714

add try catch at the first await so that we can get dump at right exc…

Do not run code style analyzers on generated files.

Fixes #12044

add try catch at the first await so that we can get dump at right exception point rather than having it as inner exception

Build updates

Our script for downloading NuGet.exe now ensures the local copy is the correct version.  Previously it assumed any local copy was the correct version.  Lead to problems when we brought down a new version that had bug fixes necessary for building the repo.