Remove looking for body statement

[dex3r]

In a previous PR, #94, a new way to create body was added: to copy the code defined in UseProvidedBody method to the target body.

I like how that works, but I don't like how that is implemented. In DelegateBodySyntaxExtractor, the code looks for memberAccess.Name.Identifier.Text == "UseProvidedBody" which is not very clean.

In BodyGenerationData record, the delegate defined in UseProvidedBody is already stored. Is that not enough to copy the source code? Maybe UseProvidedBody instead of taking Action/Func delegate, should take some "Expression" parameter, or something, so it can capture the exact code, which would remove the need to look for "UseProvidedBody" string?