DOC210/DOC211: Highlight invalid usages of <returns>

[drewnoakes]

I don't think there's a valid reason to have a <returns> element on a void typed member:

/// <returns>Nothing at all!</returns>
public void Foo();

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Nor on a type:

/// <returns>Nothing at all!</returns>
public class Foo { }

---

Nor on a field:

/// <returns>Nothing at all!</returns>
private int _foo;

[sharwell]

There are two issues here, likely with distinct diagnostic IDs:

1. DOC210: Use <value> instead of <returns> (applies to fields and properties)
2. DOC211: Element does not have a value (everything else)

[drewnoakes]

Does <returns> make sense on a non-void-returning delegate declaration?