This introduces a new core interface IDocumentOptionsProvider that
lets you provide options for documents. There's a factory to create them
to deal with the fact the implementation will be living in
EditorFeatures.Next.csproj for now.

GetUserPreferences4 will return E_INVALIDARG if you ask for a language
service that isn't registered.

* Fix crash on "is type" operator with typeless tuple expression.

Closes #13723
Fixes #13746 

Fix for tuple field locations and IsImplicitlyDeclared

Rename from AsyncBuilderAttribute to AsyncMethodBuilderAttribute

More CR feedback

Do not cache the classification service we use.  It is not safe to do so.

I'm leaving the names as is because this is hard-coded in lots of other
tests.

Add test that verifies that we don't crash if an IEditorClassificationService is exported from a language that doesn't support syntax trees.

We used to store these in multiple regstry keys, but we don't care about
that anymore since there's nothing important to maintain backwards
compatibility with. This breaks syncing of the setting between
different versions of Visual Studio, but that's not terribly important.

Include all tuple elements when expanding in the EE

These facades only need to be present next to the build task, which is
in the MSBuild/Compiler authoring.

Now that feature names aren't used for serialization anymore, we can
just get rid of the constants and use the containing type name.
Also, update more options to use nameof where appropriate.

Now that our existing options have been tagged with the appropriate
metadata, we can use that metadata to drive serialization. This
updates IOptionSerializers to make them no longer have any language-
specific metadata, and are simply driven from the metadata included
on the option.

This also renames IOptionSerializer to IOptionPersister, which is
a better name.

Now that we have an API for associating persistence information,
we can put that information on all our options we persist today.
We'll consume this in a future commit.

One current challenge of our option persistence story is the
determination of the name of an option being serialized is mixed in
with the core logic for how to serialize things to a store. This results
in some very hard-to-maintain code since the logic for an option
is spread across many different areas.

Since we only apply the options that finally changed, this behavior
should be redundant, but requires us to categorize options in a not-
obvious way.

This reverts commit b9dcaa13.

S.Collections.Immutable and System.Reflection.Metadata are seemingly
special: they're not inserted as Roslyn binaries and they're not
inserted as corefx packages. This means they won't get added to the
toolset package via either of the two previous mechanisms. Since
we don't have to worry about insertion into VS and things like binding
redirects, this change will just grab the binaries out of the output
of the build and place them directly in the output package.

Implements metadata import for tuple names in VB

Handle names correctly in long tuples in EE