forms: Provide a submission value that excludes disabled/hidden fields

Which @angular/* package(s) are relevant/related to the feature request?

forms

Description

Signal Forms currently expose form().value(), which represents the complete value of the underlying model, including fields that are disabled or hidden.

It would be useful to have a separate API that returns only values that are enabled and not hidden

For example:

const model = signal({
  name: 'John',
  email: '[email protected]',
  role: 'admin',
});

const myForm = form(model, (schemaPath) => {
  disabled(schemaPath.role);
});

Currently we can get

{
  name: 'John',
  email: '[email protected]',
  role: 'admin'
}

with myForm().value(); or model()

but we can't get this

{
  name: 'John',
  email: '[email protected]',
}

this is possible to do in reactive forms with value/getRawValue() so I think that signal forms should also provide this possibility

Proposed solution

FieldState object could include signal with value without disabled/hidden fields

so to get

{
  name: 'John',
  email: '[email protected]',
}

we could use something like myForm().submitValue();

Alternatives considered

Another possible approach would be to expose this through the existing submission API, for example:

submit(form, ({ value }) => {
  // value contains only fields that should be submitted
});