Fix S2952 FN/FP: FNs on conditional invocation and FPs on additional disposal

[martin-strecker-sonarsource]

Rule S2952 does not report on these kinds of invocations (from the sample of the rule):

  this?.fs?.Dispose(); // FN
  this.fs?.Dispose();  // FN
  fs?.Dispose();       // FN
  this!.fs?.Dispose(); // FN

Rule S2952 Does report in this case, while it shouldn't

  public void Cleanup() => fs.Dispose(); // FP: We should not report in this case as the disposal is taking place in Dispose() too
  public void Dispose() => fs.Dispose();

Originally reported by https://discuss.sonarsource.com/t/11777

[martin-strecker-sonarsource]

Peach validation revealed some FPs:

• Disposed in virtual Dispose(bool disposing) of the dispose pattern
• Diposed in DisposeAsync
• Disposal delegated in Dispose to another method.

I created a ticket for the first two patterns #6782