Allow disable in SignalFormControl

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

forms

### Description

I have two issues preventing me from using SignalFormControl in my application.

It's value is untyped in the parents value & controls. That's pretty disappointing when all our forms are typed.

But the even bigger issue is throwing an exception when trying to disable a FormGroup that contains a SignalFormControl. With this restriction we can't disable the form when the user lacks permissions, or while loading data, etc.

### Proposed solution

Allow enabling/disabling the SignalFormControl (at least from the parent form group).

And if possible extend ```AbstractConrol```. Although I assume there's probably a reason you didn't?

### Alternatives considered

Refactoring the whole form to signal forms. I don't think SignalFormConrol is useful as a bridge with these restrictions.

Start by tracing SignalFormControl's integration with FormGroup and AbstractControl in the forms package. Confirm how parent-group enable/disable state and value typing currently flow into SignalFormControl. Done means a parent FormGroup can disable and re-enable it without an exception, with typed values preserved where applicable.

Written by the indexing model from the issue text.