Removing diagnostic IDs from previous versions of the VB compiler that are no longer generated by Roslyn.

Fixes #14267.

Also move the lowering in pattern switch to the lowering phase.
As a result of this, the decision tree is now a very transient data
structure and is no longer stored in the bound tree.
Fixes #14296
Fixes #12175 

Fix CS7036 and CS1501 errors showing instead of CS0012 when calling methods taking params parameters that

take in or return types defined in unreferenced assemblies. Fixes #5043

This change enables the C# Semantic and Symbol suites.

     Background:

     As discussed in the dev team all hands all code under the GitHub dotnet foundation is using a single process for contribution, API review, infrastructure and coding style. The idea is to present a unified view to our customer and give them a single story for contributing to any project under the dotnet foundation.

     https://github.com/dotnet/corefx/wiki/Contributing#c-coding-style

     The coding style transition is automated using a Roslyn based rewrite tool:

     https://github.com/dotnet/codeformatter

     This will be applied in stages across our developer tree. Right now the focus is on the Open directory as this is what is being presented on github. Code owners will be contacted before the transition happens.

     Note: this is a soft style requirement. There are no build errors that come from this change.
 (changeset 1408227)

C#: Report a use-site error if it could be a reason for failing to implement a member of an interface. (changeset 1352026)

C#: Request use-site diagnostics while checking if type caught or thrown derives from System.Exception and report it (the use-site diagnostics) if the check failed. Fixes #132. (changeset 1351406)

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)

Reduce the variety of optimization related compilation option values used in tests to: Release, DebuggableRelease and Debug.

By default tests should use Release, which enables all optimizations.
PDB tests should mostly use Debug.
We should have targeted tests for DebuggableRelease, for optimizations that are selectively disabled to improve debuggability of release builds.

   (changeset 1312277)

C# Squiggle location for diagnostics CS0736, CS0737 and CS0738 should reflect changes made for CS0535.  So we need to squiggle the interface rather than the class.

Also remove the ImplementsInterface codefix workaround for the incorrect squiggle location. (changeset 1252265)

 Bug 911913 - Squiggle location for Unimplemented Interface Method diagnostic changed to reflect interface rather than class - matching VB implementation. (changeset 1252208)

C#: Span refinement for Overload Resolution errors. If target is a qualified name, limit span to its right most part. (changeset 1221372)