Update the Roslyn build version to 1.3.4

Delay metadata reload

1. Assert threading expectations
2. Document new variable's purpose
3. Clean up pending reloads on `Disconnect()`

Fixes #12189, and restores the behavior of the native C# language service.

The problem here is that we frequently get the file change notification
while something is still writing the file, and so we get an IOException when
we try to read it, resulting in us caching empty metadata and reporting
spurious errors.

Correctly capture the type parameter context symbol when generating SymbolId

Fix span mapping in completion commit

Update PublicAPI.Shipped.txt for what we shipped in 1.3.2

Unload with open documents

1. Use ConstructedFrom instead of OriginalDefinition to handle partially
   constructed types.
2. Always encode type parameter references using `n or ``n, since they can
   only refer to type parameters within the current symbol being encoded.
3. When *parsing* SymbolIds, *do* set the type parameter context when
   parsing types.  That way we can handle self-constructed types.  However,
   we don't want to reset the context when we're parsing out the type of a
   parameter/return type/etc, because the signature *can't* refer to the
   type parameters of *that* simple.  So, now we keep track of when the
   parser has finished parsing the top level type, and only reset the
   type parameter context while we're at the top level.
4. Add test cases for a bunch of partially constructed symbols.

(While I was here, I noticed that a GetMembers() call could be simplified to
GetTypeMembers() and a type check/cast elimiated, so I did so.  The diff
looks better with whitespace ignored because of that).

Fixes internal issue number 235912 (aka https://connect.microsoft.com/VisualStudio/feedback/details/2873787/stackoverflow-with-intellisense).

* Compute the text change in terms of the trigger snapshot
* Map those spans to the view snapshot when triggered
* Translate those spans forward to the current view snapshot

Manually updating the build version to `1.3.3.0`.

Document why the no-op virtual method still exists.

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

We already had code to deal with this case, we just hit checks before
it which threw.  The existing code needed to be modified to not modify
the collection it was enumerating though.

Fixes internal issue 233612.  Unloading a project with an open file that is
in a shared project or is linked would hit hit the exception in
CheckProjectCanBeRemoved because it still had Open documents.  Normal
projects didn't hit this because the documents were already closed by
RunningDocumentTableEvents.

Merge microupdate 3.2 into microupdate

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.

Enable release nugets in microupdate-3.2 branch

fixed 2 memory leaks

Only compute entry points when compiling everything.

Fixes #12113