Allow external value

[intellild]

Is your feature request related to a problem? Please describe.

I have a complex form with realtime preview on the left. The real data is stored model, with two view-models two-way binded to the model. useForm only support deep copy data from initialValue.

Describe the solution you'd like

Allow two-way binding from external value.

const model = reactive({ realValue: 'opt1-opt2' });

const formViewModel = reactive({
  field1: computed({
    get() {
      return model.realValue.split('-')[0];
    },
    set(value) {
      model.realValue = value + '-' + model.realValue.split('-')[1];
    },
  }),
  field2: computed({
    get() {
      return model.realValue.split('-')[1];
    },
    set(value) {
      model.realValue = model.realValue.split('-')[1] + '-' + value;
    },
  }),
});

const form = useForm({ values: formViewModel }); // all edits are synced to `model`

Describe alternatives you've considered

All these model, view-models are in different shape, so it is really a bad idea to use data from the form for preview

[intellild]

The real scenario is more complex, the model is ouside of vue and 'computed' to another framework data, for example, some chart library. There could be multiple frameworks constructs the preview