Follow-up to https://github.com/dotnet/roslyn/pull/40289

Workspace options should now be set with `Workspace.TryApplyChanges(Workspace.CurrentSolution.WithOptions(newOptions))`

Replaces the existing "Full Solution Analysis" option, with a background analysis scope to allow users to control the analysis scope for all solution crawler based background analysis.

Fixes #38429. Active file scope minimizes all the background analysis to the active files, saving on CPU consumption from background analysis on remaining files in the solution.

I have also updated up the low virtual memory listener which detects low VM and used to turn off just the full solution analysis to now set the background analysis scope to "Active file" for the current session.

1. Break the analyzer into two separate diagnostics for flagging unused and unread members. Latter rule has no code fix.
2. Remove all UI option elements for the added diagnostics and turn the rules off by default for now.
3. Bail out for invalid operations and syntax errors.
4. Handle doc comments and nameof - report unread member diagostics instead of unused member diagnostics if referenced in non-read/write context.

Analyzer flags two cases: members with no read/writes and members with only writes.

1. Members with no read or writes: `Type '{0}' has an unused private member '{1}' which can be removed.`
2. Only writes: `Type '{0}' has a private member '{1}' which can be removed as the value assigned to it is never used.`

Code fix removes the unused member declaration.
Fixes #24225

Open questions:
1. Current analyzer design uses a single code style option for all members and both the above kinds of unused members. We can potentially have multiple options, but this should probably be done based on feedback.
2. Should the analyzer use different diagnostic IDs for the above two kinds of unused members? This will mean that the FixAll experience will need multiple iterations for removing unused members.
3. Should we update the code fix (or have an additional code fix) that also updates the write references for the case (2) above? Or is it better to leave the references to break the code so the user can analyze if the value being assigned can also be removed. The PR current chooses the latter approach as it is more conservative and unlikely to cause silent breaks.

We don't need the split anymore now that we're only supporting Dev15.

Unfortunately this required the introduction of a NuGet package that
has a namespace "Workspace" to our VS project, which meant I had to
disambiguate Workspace wherever it's used in that layer. I considered
doing an extern alias instead to disambiguate, but applying that to a
ProjectReference isn't supported. That's tracked by NuGet/Home#4989.

in Dev14 these options were persisted as booleans. They are now persisted as xml in Dev15.  The fix is to not have the persistence keys overlap, ensuring Dev14 will not try to deserialize Dev15 options and vice versa

* moving naming styles types into the workspace layer.
Teaching abstract options serialization service about naming styles.

* Implementing naming styles support for editorconfig

* responding to david's PR feedback

* responding to Jason's feedback

* responding to Jason's feedback part 2

* addressing the latest set of comments from David

* addressing Jason's comments

* addressing Kevin's comments

This type should have been moved originally.

and plumb them through the UI, persistence, analyzer/fixer and
other parts of the system. update the simplifier to use the new options.
update codegen features as necessary.

They can call the public entry point instead.