Add a mock clipboard to interactive window tests

Disabling flaky tests. These three tests failed on an internal run.

Disabling flaky tests from http://dotnet-ci.cloudapp.net/job/roslyn-internal_master_win_rel_unit32/7/

Optimistically classify the 'await' keyword

Fixes #2301

Unlist delegates from the VB completion list

Fixes https://github.com/dotnet/roslyn/issues/4208

Fix indentation when pressing ENTER in a partially completed from clause of a query expression

rename WithDeterminism to WithDeterministic

Fix build break by adding missing parens to Vbc task

Re-enable a couple of tests

Revert "Inherit Global Usings from previous submissions"

Inherit Global Usings from previous submissions

In Visual Studio 2013, we would always indent to the start of the 'from' keyword when pressing ENTER inside of a from clause. For example:

```C#
var q = from x
        |
```

and

```C#
var q = from x in
        |
```

Unfortunately, we regressed that behavior in Visual Studio 2015. It now does this:

```C#
var q = from x
			|
```

This change restores the VS 2013 behavior by adding a special indent block operation specifically for ```FromClauseSyntax```. However, it also continues to support nested query formatting, which we improved in VS 2015:

```C#
var q = from x in
		    from y in args
		    select y
		select x;
```

Improve compiler behavior around stack overflow caused by long binary expressions.

deal with cases where item in table control is not associated with any project or document

Add PDB format option to /debug flag

Look at the usings for each submission as we visit that submission.  The
mental model is a chain of ```InContainerBinder```s, but we don't actually
instantiate the chain for perf reasons.

TODO: Some tests are failing because of the new semantics.  The main issue
is that usings can now hide members (not just types).  No corresponding
issue exists in C# because usings can't appear within types.

Use correct span to determine block kind

Fixes #5395.

Adjusted Binder, Optimizer, Flow Analysis, code generator and majority of bound tree visitors to not use recursion to handle binary expressions nested on the left side of another binary expression.
Adjusted majority of bound tree visitors to detect that stack overflow is about to happen while an expression is being traversed and report a diagnostic pointing to the expression at fault instead of crashing compiler.

Fixes incorrect codegen where locals could be optimized across implicit branches

Adjustment of the fix for #4471

Property support inference in async lambda/delegates

Fixes #4486

Unbreak End Construct around an broken code scenario

Fix the AnalyzerDependencyChecker to ignore mscorlib

Disable more flaky tests in InteractiveWindowTests

These tests access the clipboard directly in the unit tests and hence
have flaky behavior across machines. Disabling.

See https://github.com/dotnet/roslyn/issues/5544

process all attributes in XML documentation comments

Don't simplify Nullable<T> to T? inside nameof expressions