Updates Concord APIs in Roslyn to add new field "CustomTypeInfo" which is passed between an managed expression complier and a result provider.
This new field is a new value type "DkmClrCustomTypeInfo", which is used to convey complier specific type information that is not represented by .NET data types (such as C#'s 'dynamic' type).
In Roslyn, this commit also updates the ResultProvider's mock implementation of the Concord API and fixes all affected callsites.

The API Environment.CurrentDirectory is not available on CoreFX.
Switching all uses to Directory.GetCurrentDirectory which is an
equivalent API (it is actually how Environment.CurrentDirectory is often
implemented).

closes #1829

This changes the compiler APIs to no longer use
RuntimeVersion.GetRuntimeDirectory to find the path to mscorlib and
System.dll for the following reasons:

- This API is not available in CoreFx and hence blocks our transition.
- This behavior of implicitly referencing mscorlib doesn't have a
logical equivalent in coreclr where there may be no reachable mscorlib
on the machine (think Linux).

The compiler now takes the SDK search directory as a paramater.  The
consmer will be responsible for feeding down the correct value to the
compiler.

This is the first step in resolving issue #1939

closes #1943

Add MSBuild support for AnalyzerDependency items

Set correct checkmarks in "Set Rule Set Severity"

Set correct path to linked rule set file.

Slimmed down toolset.sln

It now encompasses the actual toolset portion of Roslyn.

Ensure that IOFailure_OpenOutputFile unit-test passes in presence of localized resources.

Fixes #1394.

Propagate Debugger… attributes from async/iterator method to the corresponding state machine MoveNext method.

Propagate Debugger… attributes from async/iterator method to the corresponding state machine MoveNext method.

This addresses issue #807.

PDB verification helper cleanup

added error source support

...

now, error list will have column (which is off by default) that shows source of each errors in a format "assembly name" or "assembly name [vsix name]"

now, error list will have column (which is off by default) that shows source of each errors in a
format "assembly name" for analyzers node. and "assembly name" [vsix name] for vsix

Fix cast simplification within ConditionalAccessExpression.

Handle ConditionalAccessExpressionSyntax expressions within speculation analyzer to ensure that semantics of the conditional access expression and the WhenNotNull part don't change on cast simplication.

Fixes #253

Merge pull request #1914 from shyamnamboodiripad/SimplifierAnnotationForImplementInterfaceThruMember

Add simplifier annotation to cast expressions generated using syntax generator.

This ensures that code fixes such as Implement Interface Through Member never generate casts that user has to simplify in a subsequent manual step.

Fixes #472

Port CA1309 (Use Ordinal StringComparison) to System.Runtime.Analyzers.

Add support for highlighting written references differently than read references.

Add Visible=false metadata to one of the instances of Errors.vb

This prevents it from being listed twice in Solution Explorer.

Fixes #1876.

The fixer for this rule delves into syntax significantly and so cannot be written with just syntaxgenerator. I've refactored the fixer implementation to share some code between the C#\VB fixer.

This prevents it from being listed twice in Solution Explorer.

Fixes #1876.

Handle ConditionalAccessExpressionSyntax expressions within speculation analyzer to ensure that semantics of the conditional access expression and the WhenNotNull part don't change on cast simplication.

Fixes #253

This ensures that code fixes such as Implement Interface Through Member never generate casts that user has to simplify in a subsequent manual step.

Fixes #472

Localization fix for DiagnosticLocalizationTests.TestDiagnosticLocalization: Use the CurrentUICulture as the default culture, not "en-US" culture.

Fixes #1006 

Adding a document describing the semantics of analyzer actions and the c...

Add simplifier annotation as part of Add Using fix

Fixes #1893

Also add simplifier annotation to using directives / imports statements generated by the code generation service.

Adding a document describing the semantics of analyzer actions and the contract between the API and implementations.

Add simplifier annotation on using directives generated via the Add Using fix so that generated directives are already simplified (in the case where using is generated inside a namespace declaration) without the user having to simplify manually in a subsequent step.

Note: I also added the annotation inthe corresponding VB fix for parity. However, this should be a no-op for VB since VB only supports file-level namespace imports.

Fixes #1893

Fix spelling mistake.  Add a 'none' kind to HighlightKind to indicate you want the default highlighting for the span.

Make DiagnosticAnalyzerExtensions.GetDiagnosticAnalyzerCategory async to avoid force computing registered analyzer actions in the IDE.

Use SymReader from debugger (that supports CDI from EnC pdbs)...

This involves a couple changes:

- Fix signature of IENCSymbolReaderProvider.GetSymbolReader
- Remove all of our "fallback" SymReader creation logic and use
  ISymUnmanagedReader3 when getting custom debug info

Clean up local scopes produced by PdbToXml and update tests accordingly