Signal forms: Composing components without nesting the form model

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

forms

### Description

Currently I have two models:
```ts
export interface NumberRange {
from: number;
to: number;
}

export interface ExtendedNumberRange extends NumberRange {
includeMissing: boolean;
}
```
Using signal forms I created a component for `NumberRange` and because it has built in validation (like valid range) it isn't a `FormValueControl` and accepts a field as input and exports a schema to use with `apply`.

Then I wanted to create `ExtendedNumberRange` component using `NumberRange` component.
First I did:
```ts
export const extendedNumberRangeSchema = schema((path) => {
apply(path, numberRangeSchema);
// other validations specific to ExtendedNumberRange...
});
```
Which allows composing the schema nicely.
Then I wanted to create the component. At this point I got stuck... Here are the options I thought about:
1. Change `ExtendedNumberRange` to be nested - but that's annoying as the server accepts a flat model and I want to avoid mapping as much as possible:
```ts
export interface ExtendedNumberRange {
range: NumberRange;
includeMissing: boolean;
}
```
2. Accept `FieldTree` and pass it as is to the number range component as is. Unfortunately it fails with a type error.
3. Accept `FieldTree` but there is no way to check which type it is as `'includeMissing' in field` will be false due to proxy and anyway probably won't narrow the type correctly.

So I am stuck with option 1 which is a shame...

Here is a stackblitz with option 2 which doesn't work (comment the number range component usage in extended number range component for it to run):
https://stackblitz.com/edit/bw2bfa5z?file=src%2Fmain.ts

### Proposed solution

Somehow allow composing form based components in a way that supports inheritance in model. Either fix option 2 types problem or somehow allow something along the lines of a `linkedForm` or maybe there is a way which I am not aware of to make 3 work with the union?

### Alternatives considered

1. Use nesting in the form model and add a mapper from model to form model and vice versa (can be annoying when the form has a large model)
2. Use `FormValueControl` but then validation will be inside the component and not in the schema which will cause a lot of other problems...