Prevent SemanticModel.GetSymbolInfo from crashing when Me/this is used outside of a valid member context. (changeset 1367667)

***NO_CI***
 (changeset 1356181)

Abbreviates the public VB-specific types (e.g. VisualBasicSyntaxTree -> VBSyntaxTree) in accordance with the .NET Class Library Guidelines to avoid overly lengthy names and consistent with the conventions used in other APIs (e.g. VB CodeDom). (changeset 1348499)

This shelveset implements following changes to metadata reference compiler API in order to remove duplication in the public surface and prevent users from unexpected metadata lifetime issues:

     1) MetadataImageReference and MetadataFileReference overlap
     Currently MetadataImageReference can be constructed from a Stream. MetadataImageReference supports metadata prefetch (reading the blob into memory and close the underlying stream) as well deferred reading (no content is read until the reference is consumed during compilation). MetadataFileReference only supports deferred reading.

     Lifetime of MetadataFileReference is non-deterministic, the underlying file is locked until no references exist and we GC the metadata.  On the other hand, it is possible to construct MetadataImageReference in such a way that allows controlling the underlying resources deterministically.

     Remove MetadataFileReference, use MetadataImageReference instead.

     2) Lifetime management
     AssemblyMetadata and ModuleMetadata objects hold on resources and implement IDisposable. When using MetadataFileReference constructors and some MetadataImageReference constructors to create references the underlying metadata objects are created implicitly and the user doesn’t have a way to explicitly dispose them.

     Make MetadataImageReference constructors internal and instead add factory method GetReference on AssemblyMetadata/ModuleMetadata. The usage pattern is:

     using (var metadata = AssemblyMetadata.CreateFromXxx(…))
     {
         var compilation = CSharpCompilation.Create(syntaxTrees, new[] { metadata.GetReference() });
         …
     }

     In addition the shelveset makes MetadataImageReference internal and adds the following convenience APIs, that are not the most efficient but are very convenient, easy to discover and safe to use for customers that don’t wanna explicitly manage the lifetime of metadata objects. (changeset 1345987)

Similarly for DynamicType and PointerType. (changeset 1345275)

made compiler error message to not include namespaces in most cases. this should make parsing error message a bit easier. (changeset 1334448)

- For Query Expressions, limit the span to operator(s) token(s).
- For other expressions, exclude arguments from the span. If target is a qualified name, limit span to its right most part. (changeset 1220484)

Public API Change: Rename IFieldSymbol.AssociatedPropertyOrEvent , IMethodSymbol.AssociatedPropertyOrEvent and INamedTypeSymbol. AssociatedEvent APIs to AssociatedSymbol to accommodate for future language changes. (changeset 1210026)