Improve the description of `Delegate.DynamicInvoke`

The `DynamicInvoke` [summary](https://github.com/dotnet/dotnet-api-docs/blob/2c2a97525d0e95f5ce3460106c4047920720e5ed/xml/System/Delegate.xml#L1955) is not helpful at all for someone that does not know the difference between `Invoke` and `DynamicInvoke`.

Marc Gravell gave a great explanation in StackOverflow about the difference in behavior between the two: https://stackoverflow.com/questions/12858340/difference-between-invoke-and-dynamicinvoke

We should improve the official documentation to include a similar explanation, at the very least in the remarks section. Ideally, the summary should _not_ describe the API with the same words used in the API's name.