fix fallback for suspended methods

[ondrej-hrstka]

Fixes #7101

[dstepanov]

Why does this not work by default? KotlinInterceptedMethod should fill the future if the value is not the coroutine:

  public CompletableFuture<Object> interceptResultAsCompletionStage() {
        @SuppressWarnings("unchecked")
        CompletableFutureContinuation completableFutureContinuation = new CompletableFutureContinuation((Continuation<Object>) continuation);
        replaceContinuation.accept(completableFutureContinuation);
        Object result = context.proceed();
        replaceContinuation.accept(continuation);
        if (result != KotlinUtils.COROUTINE_SUSPENDED) {
            completableFutureContinuation.resumeWith(result);
        }
        return completableFutureContinuation.getCompletableFuture();
    }
    ```

[ondrej-hrstka]

@dstepanov : The problem is the fallback method. The 'MethodExecutionHandle' is located in 'findFallbackMethod' method. So for that one, there is no instance of 'KotlinInterceptedMethod'