Since commit 842622bf8bea782e9d9865ed78b0d8643f098122 adding support for
overloading interface methods, a `using` directive is emitted for any
interface method that does not require emission of a trait method,
including for methods that define a method body.
However, methods directly specifying a body (e.g., via the `methodBody`
parameter of `InterfaceMethod`) are implemented directly in the
interface class and are therefore not present in the associated trait.
The generated `using` directive then referes to a non-existent method of
the trait, resulting in an error upon compilation of the generated code.
This patch changes `DefGen::emitTraitMethods()`, such that
`genTraitMethodUsingDecl()` is not invoked for interface methods with a
body anymore.
8eacea9934