Annotates benchmark snippet.

Its value sets the scope name of the snippet.

The following declaration:

@benchmark("arrays.forloops")
public void snippetMethod(int[] xs) {
  // ...
}

declares a benchmark snippet, equivalent to:

performance of "arrays" in {
  measure method "forloops" in {
    // ...
  }
}

Note that method annotated with @benchmark should be public and have a single argument of type T, such that it corresponds to the type of the generator declared in the @gen annotation.