Missing short form delegate instantiantion

These options are missing and an explanation on the difference between these and the presented ones:

```csharp
D cd1 = new C.M1; // static method
D cd2 = new t.M2; // instance method
D cd3 = new cd2; // another delegate
```

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#### Document Details

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* ID: 6d5a9d5f-36b3-be69-bbf8-93fb75237d1e
* Version Independent ID: 02628e27-dd25-fb6b-89a9-21c5e900120f
* Content: [Delegates - C# language specification](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/delegates)
* Content Source: [spec/delegates.md](https://github.com/dotnet/csharplang/blob/main/spec/delegates.md)
* Product: **dotnet-csharp**
* Technology: **csharp-spec**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **wiwagn**