Resolved arguments contain extra values

[HitkoDev]

Describe the bug
Params with @Args decorator contain all arguments, not just arguments defined in target type.

type-graphql/src/helpers/types.ts

Line 105 in 59ef256

return Object.assign(new Target(), data);

To Reproduce

@ArgsType()
class TestArgs {
  @Field(() => String) foo: string
  @Field(() => String) bar: string
}

@Resolver()
class TestResolver {
  @Mutation(() => String)
  test(
    @Arg('extra') extra: string,
    @Args('test') test: TestArgs
  ) {
    console.log(test)
    return extra
  }
}

Expected behavior

{
  "foo": "value",
  "bar": "value"
}

Current behavior

{
  "foo": "value",
  "bar": "value",
  "extra": "value"
}

Enviorment (please complete the following information):
Every environment, all package versions

[MichalLytek]

Partially related to #263 but in that case it's working as designed - you shouldn't mix the two ways of registering args.

If you need to add extra argument, just extend TestArgs class.