Merge dev15.7.x to dev15.7.x-vs-deps

* Fixes mapping of active statement when changing ctor body from block to expression

* Fix GetAllAddedSymbolsAsync.

- Recover from unexpected exceptions.
- Ignore documents that do not belong to the project being emitted during EnC (these could be e.g. speculative documents created by code fix preview).

Change fields of DocumentAnalysisResults to properties to workaround a bug in the VIL that causes evaluation to fail on them, thus making it hard to see the values while debugging Roslyn.

Enable NuGet package signing

Merge dev15.7.x to dev15.7.x-vs-deps

* Update Roslyn snapshot when editorconfig is updated. for now, it only updates when editorconfig is saved.

* added more comments

* addressed PR feedbacks

In Object serialization, do not keep track of non-reusable green nodes.

Merge dev15.7.x to dev15.7.x-vs-deps

Fix publish error

Merge dev15.7.x to dev15.7.x-vs-deps

Build NuPkg on Unix

Change our Unix builds to create the set of NuGet packages that are needed for
source build.

LOC CHECKIN | dotnet/roslyn dev15.7.x-vs-deps | 20180409

Merge dev15.7.x to dev15.7.x-vs-deps

Move to dotnet pack

Using the console outputs warning messages which MSBuild interprets as a
build warning and we fail the build due to warn as error being enabled.
Just hide the warnings until we can find a replacement setting.

https://github.com/NuGet/Home/issues/6817

Moved the last of our NuGet package creation over to dotnet. Deleted all
remaining infrastructure for using NuGet.exe.