Keep default values for fields if parameter isn't provided

[LeStegii]

• Don't overwrite values if parameter isn't provided
• cleanup some code

[Clashsoft]

LGTM, but there was a suggestion for another usecase that could be integrated. Right in this case:

class Component1 {
  @Param("foo")
  IntegerProperty fooProperty;
}

class Component2 {
  IntegerProperty fooProperty;
  // ...
  show(component1, Map.of("foo", fooProperty));
}

There will be an error. In this case it makes sense to treat the attribute as a regular object instead of a WritableValue. I am unsure about other cases involving final, or if bind or even bindBidirectional might be wanted. But I guess as a default behavior, simple assignment should be possible.

[LeStegii]

I changed it so that the special logic for WritableValues only applies if the provided parameter isn't a WritableValue itself.
If so, the basic logic will be used instead.