removed semantic version tracking code which recently caused some issue on RPS test. this code is already removed from master (15.5)

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.

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

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.

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.

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.

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.

ThemeColorFixers was running during ASL for some users and forcing the editor to compose at that time. Instead, we wait until a text editor of the appropriate content type has been opened.

Addresses devdiv bug https://devdiv.visualstudio.com/DevDiv/_workitems/edit/130129

We've received watsons that indicate that a VB file is being set as the
"context buffer" for C# debugger intellisense. It appears that this
would only happen if the debuggered called us with a buffer of the wrong
content type. Add an assertion that the content type is correct.

Related to
https://devdiv.visualstudio.com/DevDiv/_workitems?id=397711&_a=edit&triage=true

Fixes
https://devdiv.visualstudio.com/DevDiv/_workitems?id=391624&_a=edit

- Inline Rename fields now consist of a themeable/customizable
background, foreground, and border. The border is used in High Contrast.
- Resolved and Unresolved conflict borders can now be themed &
customized.
- Resolved and Unresolved conflict borders now have different dash
styles so they are distinct from each other and regular Inline Rename
fields. The Dashboard shows a key indicating which type of conflict
corresponds to which border dash style.

Before this change we were immediately trying to add file watchers
on the UI thread when we added a new analyzer. This can get delayed
because of slow disks, or because the file watcher service's lock is
held by a background thread. There's no reason to do it until we are
actually observing and loading the analyzer, which typically happens
on a background thread.

FileChangeTracker is subject to the evils of the file system, and
thus we swallow a few top-hitting exceptions that we shouldn't be
crashing on. For FileNotFoundException, we'll still log a non-fatal
telemetry event so we can continue to drive some fixes into the core
VS service.

We were creating a bunch of tasks on the thread pool, all of which
ultimately contended on the single lock that exists inside of the
current implementation of IVsFileChangeEx. That's silly, so let's just
only try to do one of the background subscriptions at a time.

The solution build manager will handle the opted out ones, but not the failed design time build ones.

Fixes #19407.

We believe that the primary cause of this exception (some issues around
projection buffers) was worked around in d8f8dad3 but we're still
seeing issues so that's not the case. I'm also further not convinced
that change helped at all, because in many case we already fork
buffers to work around the same issue.

Don't try to create a deferred project for a project reference if the design time build
failed, or the project system opted out of deferred projects for this project.

Move initialization earlier.