Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=233669.

Fixes #14365.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems?id=217718.

Provide an API to get unreferenced assembly identities obects from the diagnostics reported about them.

Use tuple syntax in the compiler

added Language property to ParseOption and CompilationOption

property name followed the compiler code base pattern.

Support setting if an anonymous type's properties are mutable or not.

(thank you @keyboardDrummer!)

* CommonPEModuleBuilder refactoring

* Renames

* Use CommonPEModuleBuilder instead of IModule

* Remove IModule

* Move GetFiles to module builder

* Remove IAssembly

* Add comments, PR feedback

* Resolve merge conflicts

* Implement source link feature

* Fix CommonCompiler to open source link stream, add E2E tests

* Reduce code duplication across VB and C#

* Add support for a new ProjectShimFactory to be consumed by CPS.

1. IProjectShim and IProjectShimFactory are the primary interfaces being introduced that CPS will use to forward project system changes to workspace hosts.
2. Refactored the UpdateOptions code in AbstractRoslynProject and sub-types so that it can be shared with the new project shim.

TODO: Add IVT to CPS binaries to enable consuming these APIs (need to follow up with DavKean)

* Add support for a new ProjectShimFactory to be consumed by CPS

1. IProjectShim and IProjectShimFactory are the primary interfaces being introduced that CPS will use to forward project system changes to workspace hosts.

2. Refactored the UpdateOptions code in AbstractRoslynProject and sub-types so that it can be shared with the new project shim.

3. Add IVT to CPS projects to enable consuming these APIs.

* Fix tests

* Add tests for new CPS project shim.

* Fix the tests and update the Shim factory API to take CommandLineArguments.

* Fix VSI test - VB compilation options must also contain latest parse options

* Some more code refactoring to ensure that for the CPS shim we avoid getting properties through the hierarchy while creating the shim and adding new source files.

* Some more code refactoring to address review feedback:

1. Rename IProjectShim and IProjectShimFactory to IProjectContext and IProjectContextFactory respectively.
2. Add a new sub-type of AbstractProject, namely "AbstractLegacyProject", for legacy C# and VB project system shims. All the Hierarchy accesses for computing properties have been moved to this sub-type.
3. Move legacy project system specific interface implementations (IVsHierarchyEvents, IIntellisenseBuildTarget and ICompilerOptionsHostObject) to AbstractLegacyProject.
4. Merge AbstractRoslynProject into AbstractProject - the only addition in AbstractRoslynProject seem to be support for VsENCRebuildableProjectImpl, which was anyways an optional field.

* Change the name of the flag taken by AddSourceFile to "isInCurrentContext"

* Address review feedback

* Fix tests broken by last commit

* Further cleanup of options setting infrastructure

* Minor refactoring of the Options setting APIs

Also address review comments with more tests

These internal methods are mirror of their public counterpart minus feature flag check, they are
intended to be used by IDE built-in analyzers.

Revert "Revert "Revert "Revert "*DON'T MERGE INTO MASTER* Hide IOperation API behind a feature flag""""

This reverts commit d4d502e4.

This reverts commit c6a1c2c8.

Add support for an OperationTreeVerifier - test only OperationWalker to dump operation tree. (#11918)

The dump approach should enable to us to (relatively) easily extend the existing C# and VB binding tests to verify the operation tree.
I have moved the existing IOperation tests to the dump approach and also added couple of additional tests to demonstrate how to write these tests for entire method body operation tree verification.