Build NuGet with correct prerelease tags

Need to thread through the official build value to ensure packages are
built with the correct prerelease modifiers (beta, async, etc ...)
instead of simply dev.

Make sure we always subscribe to shared hierarchy eventing

Fix race condition in SolutionExplorer_InProc.OpenFile

This change updates the file open implementation use VsShellUtilities.OpenDocument.
DTE plus waiting for the active window title alone proved insufficient, where some
tests were incorrectly operating on the previous active document.

Fixes #19191
Fixes #26037

Enable NuGet package signing

* 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.

In d9e30021 I restored the code that was subscribing to IVsHierarchy
event notifications to know when shared contexts change. Unfortunately
it was put in the event handler for IVisualStudioHostDocument.Opened,
which only runs when the document is being opened that was already
part of the workspace. If the reverse order happens: a file is already
open, and only _then_ added to the workspace, the code was skipped.

Curiously, Workspace has an overridable method OnDocumentClosing which
you can use to hook calls, but not an equivalent OnDocumentOpening. It's
unclear to me if this design was something we want to extend (it's a bit
strange) and so I'm not touching that for now.

Fixes dotnet/project-system#3467.

Build NuPkg on Unix

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

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.