CA2213: Handle overriden DisposeCoreAsync / DisposeAsyncCore

[MartyIX]

Follow-up to #6976

This PR fixes up CA2213 implementation to handle the following use case:

using System;
using System.Threading.Tasks;

class A : IAsyncDisposable
{
    private readonly object disposedValueLock = new object();
    private bool disposedValue;
    private readonly Inner innerA;

    public A() 
    {
        innerA = new Inner();
    }

    protected virtual async ValueTask DisposeCoreAsync()
    {
        lock (disposedValueLock)
        {
            if (disposedValue)
            {
                return;
            }

            disposedValue = true;
        }

        await innerA.DisposeAsync().ConfigureAwait(false);
    }

    public ValueTask DisposeAsync()
    {
        return default(ValueTask);
    }
}

class B : A
{
    private readonly object disposedValueLock = new object();
    private bool disposedValue;

    // Newly, we want to test that no diagnostic is reported on this line.
    private readonly Inner innerB;  /* <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< */

    public B() : base()
    {
        innerB = new Inner();
    }

    protected override async ValueTask DisposeCoreAsync()
    {
        lock (disposedValueLock)
        {
            if (disposedValue)
            {
                return;
            }

            disposedValue = true;
        }

        await innerB.DisposeAsync().ConfigureAwait(false);

        await base.DisposeCoreAsync().ConfigureAwait(false);
    }
}

// Declares an IAsyncDisposable type.
class Inner : IAsyncDisposable
{
    public Inner() 
    {
    }

    public ValueTask DisposeAsync()
    {
        return default(ValueTask);
    }
}

That is innerB is now marked as not disposed because its DisposeCoreAsync method has in its method signature override instead of virtual.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.49%. Comparing base (43709af) to head (3c81f1d).

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #7347    +/-   ##
========================================
  Coverage   96.49%   96.49%            
========================================
  Files        1443     1443            
  Lines      345799   345885    +86     
  Branches    11374    11374            
========================================
+ Hits       333665   333771   +106     
+ Misses       9251     9233    -18     
+ Partials     2883     2881     -2     

[MartyIX]

@buyaa-n Could you please take a look if you have a moment?

[MartyIX]

@drewnoakes Could you please take a look?

[MartyIX]

@Evangelink Could you take a look please?

[Evangelink]

LGTM

[MartyIX]

@buyaa-n @Evangelink Could the PR be merged?

[Evangelink]

@buyaa-n this seems low risk for me to merge.