Updating the build property from 'VisualStudioInstallDirectoryFromRegistry' to 'IsDev15BeforePreview4'

Fix #12818

* CommonPEModuleBuilder refactoring

* Renames

* Use CommonPEModuleBuilder instead of IModule

* Remove IModule

* Move GetFiles to module builder

* Remove IAssembly

* Add comments, PR feedback

* Resolve merge conflicts

Use ByPass to run Powershell

reduced a bit more allocations

Updating the build property from 'VisualStudioInstallDirectoryFromRegistry' to 'IsDev15BeforePreview4'

Make IDkm* stub interfaces internal...

Report errors for new features unsupported in expression trees.

These are not intended to be public APIs at this point (they'll eventually
be added to Concord as public APIs).

Add support for embedding C# source in portable pdb

Updating Roslyn to consume the Preview4 VSSDK packages.

Don't run VB enum completion after dot

Commit C# completion on colon

Add parsing of NuGet.Config files to RepoUtil and other work.

Members after dot are now provided by SymbolCompletionProvider. Fixes

Unwrap arrays when determining whether to show the builder for lambda
expressions.

Use nuget restore to determine the exact dependencies we need to insert into VS.

Conflicts:
 src/Workspaces/Core/Portable/WorkspacesResources.resx

Handle pointer and error types in NormalizeTaskTypes

Fix #12755

Rewrite make async

Fixes #12578

It looks like a couple of changes brought them out of sync
and VS really dislikes it.

The RepoUtil tool will now include NuGet feed information in the output
for the 'consumes' command.
Added a mechanism for excluding project.json files from being included.
Package conflicts will no longer result in an unhandled exception, instead
it will output a list of the conflicts.

Add IVT to Orchestrator UnitTests

Fix our MSBuild logic around signing

Make EncodedStringText fallback encoding lazy

get callstack on codefix crash

Follow-up on some recent changes in C# compiler.