Couple of items:

- Plumb AssemblyInfo through the code base
- Remove most usages of ResultsFileName from caching layer

Now factors in the maximum windows command line length.  It also has
improved logging.

Turn off hard-linking during the build

We turned on hard-linking to reduce copy and build time, however,
this would result in behavior where copying a NuGet binary from .nuget/packages to the output directly which was then subsequently overwritten with a different version would result in the .nuget\packages folder to be corrupted because they were now linked.

Move to RC toolset

more allocation reduction.

This changes the toolset we use to build Roslyn on our developer boxes to 1.2.0-rc.  Very close to release, need to make sure we're eating the latest brand of dogfood 😄

Merge stabilization into master

Only collect archives in the case of aborted or failed runs.

Update what we archive after a run.

Fix for 7845: add DynamicAttribute to event with dynamic type

Add member visibility modifiers

- avoid instantiating nullable type when doing operator overloading on enums
- avoid instantiating generics when checking for impossibly rare case of duplicated interface implementations
- skipping materializing of sequence point array

Fix for #7809: check for use-site errors on attribute before synthesizing

No functional change here.

Removing the 'System.Diagnostics.Process' dependency from 'InteractiveFeatures'

Fix for #9167: async and iterator rewriters do not require optional attribute types

Fix for #9167: async and iterator rewriters do not require CompilerGeneratedAttribute or DebuggerNonUserCodeAttribute or DebuggerHiddenAttribute

allow cancelation exceptions through the PE stream diagnostic filter

Pool per-analyzer state instances across CompilationWithAnalyzers ins…

Watch xUnit processes for dumps in RunTests

Add skeleton assembly logging

Fix issue where we weren't offering 'generate variable'

Fixes #8358

Revert "Revert "Improve the Generate-Variable code-actions menu experience.""

Fixes: https://github.com/dotnet/roslyn/issues/6979