Breaks the internal GTD infrastructure into seperate symbols for
determining the navigable symbol at the caret position and performing
the navigation.

this is port of https://github.com/dotnet/roslyn/pull/20968 to dev15.3.x

If you had a F# project opened with the new project system, it'd supply
an output directory which other projects (like C#) could reference.
If you had a C# project that referenced the F# project, any attempt
to get the C# compilation would crash because we can't actually produce
F# compilations. The fix is simple: don't convert from metadata
references.

If we're going to require it, let's at least crash with a useful
exception instead of a null ref.

Other components should be able to access this too, especially since
the workspace itself isn't always there.

code

If you create an elision buffer, there's no way to disconnect the
elision buffer from the underlying buffer once you're done with it,
causing the elision buffer to leak. It's possible to disconnect
projection buffers, so we use them to work around this limitation.

When we create a projection buffer, that buffer is strongly held by
the underlying buffer, which means we have a memory leak unless we
disconnect it by unmapping all spans. This also causes problems because
bugs in the editor around projections can then cause crashes when we
didn't actually need the buffers anymore.

See #20412

The VisualStudioRuleSetManager is a singleton that acts as a cache
of RuleSetFiles and also manages the lifetime of file watching. We
never cleaned that up when we shut down VS, so we leaked a bunch of
file watchers, which would throw during finalization asserting they
weren't cleaned up and bring down the process with it.

Removing the old style of package publishing. The official build definition will now control
uploading packages to the DevDiv feeds.

Revert "Merge pull request #20558 from Pilchie/Fix19968-DuplicateSourceAndAdditionalFiles-DistinctIds"

This reverts commit 6f5b2d47, reversing
changes made to 66362df5.

Fixes crashes associated with InvisibleEditor

Fixes #20149.

If the user closes a textview while completion is filtering, it's possible for the filtering task to ask for a Document before it gets cancelled, resulting in a crash. To prevent this, restrict Controller.GetDocument() to the foreground thread.

This is a breaking API change.  Need to decide if we want to take it or
not.

Turns out we could end up with the same IVisualStudioHostDocument
for both, if they are both added.

Fixes #19968.