Fix a couple of build issues

Integrate GitLink into the Roslyn build

Simplify the api and implementation for IOptionProviders

Order DocCommentHandler after Commit and Completion handlers.

This adds source server support to our binaries by means of GitLink.

Implementation of issue #13585

add options back to diagnostics

Move us to the latest version of the Nuget.VisualStudio api.

Provide a user facing option to control the 'add-braces' code style feature

Update our code so that Suggestions show up in the scroll bar on the right. 

Support undo'ing the File-Add caused by 'Move type.

Prior to C# 7 we tried to avoid giving duplicate errors
when the user used a variable before it was declared (which
is both a use-before-declared and a use-before-assigned error),
but the line here is blurred with local functions, which can
use variables before they are declared in subtle ways that can't
be detected based on declaration order in syntax.

It may be possible to provide the earlier behavior, but the
current optimization is definitely insufficient and hides
legitimate errors in user programs.

Fixes #15298
Fixes #15322

Merge dev15-rc2 into master

The throwing version of a TraceListener is how we prevent Debug.Assert dialogs popping up on our Jenkins runs.  The separation of our tests into a proper portable and non-portable subset revealed that we only had a desktop version of this class.  A portable version is needed to get the same behavior for CoreCLR unit tests.

This is a centrally controlled property.

This setting controls binary deployment hence it needs to be centrally
managed to help ensure we have a correct build.  Custom projects can
continue to control this setting themselves.

It was incorrectly labeled as a VSIX.

Optimizer should classify assignments to PseudoVariables as indirect assignments

Remove blocking-wait from completoin when caret is moved.

Address issues with SemanticModel behavior around TupleElementSyntax.