Fixes https://github.com/dotnet/roslyn/issues/37913

Fixes https://github.com/dotnet/roslyn/issues/37252

Also add a few more places where we need to wrap symbols.

It turns out for methods we already had
RemoveInaccessibleAttributesAndAttributesOfTypes but had accidentally
created another helper for filtering out attributes from parameters
that more correctly should have used that. This also observed that we
didn't have a helper for IParameterSymbols to do the same thing.
We did have one that filtered but not one that removed innaccessible
parameters, which was actually a bug.

We had a helper for 'create an IMethodSymbol with certain changes', but
it didn't have quite enough that we could use it in more places. Also
inline it into the single caller.

- Ensure we show the ? in all the appropriate places
- Ensure we don't spit ? if we shouldn't
- Ensure we drop ? for the special case of the ToString return

for now, it only reports method calls and member references from metadata reference.

it reports data as hash value to protect privacy

If we have inferred the thing to the left of a ?? is a reference type,
we can annotate it; we didn't update that yet in the type inferrer
though until we had the ability to properly remove the ? if the
user wasn't in the right context. The parent commit of this commit fixes
that so we can fix this now.

At this point, the flighting controls we have aren't really useful
anymore: we want this on for everybody unless the opt out, and that
opt-out would be specific to certain users that are running into issues
with the new system to keep them unblocked. I'm keeping this a per-
machine setting (that doesn't roam) because it's really repo or VS
version specific.

* Cleanup

* Optimize memory allocation of LCS algorithm

Fixes https://github.com/dotnet/roslyn/issues/36044

This code is assuming that given a token, we can chase up and find
a node that surrounds a span. Using FirstOrDefault meant if we couldn't
find one we'd pass null to GetSemanticModelForNodeAsync which would
promptly throw an exception. This will still throw exceptions but at
least will throw earlier.

I had to look at this code to understand exactly what can and can't
be nullable; since I think I've figured it out I'll annotate
accordingly.

Fixes https://github.com/dotnet/roslyn/issues/30325

Merge NullableAnnotation.NotApplicable and Disabled to None, and rename NullableFlowState.NotApplicable to None for consistency.