docs-bug(chips): the "form example" is not fully related to forms

### Documentation Feedback

We have `chips-form-control-example`, `chips-reactive-form-example` components that intend to illustrate how chips interact with the form control.
I see 2 problems here.

1. The interaction with `mat-chip-grid` is happening not fully through the formControl. For now the source of chips's list is `keywords` signal, not the formControl: `@for (keyword of keywords(); track keyword) {`
It seems we should take the formControl as the source of chips's list (not the signal): `@for (keyword of formControl.value || []; track keyword) {`
Moreover we could get rid of the signal, because the goal of the example is to show the interaction between the formControl and the chips in the template.

2. These two examples of `chips-form-control-example` and `chips-reactive-form-example` components duplicate each other. They have the same logic inside of components classes. So it seems we could leave only one of these two examples.

### Affected documentation page

https://material.angular.dev/components/chips/examples

Start with the chips-form-control-example and chips-reactive-form-example components referenced in the issue, and inspect the examples shown on the chips documentation page. Compare their classes and templates; done means the chips list is demonstrated through the formControl rather than the keywords signal and the duplicated example is removed or consolidated.

Written by the indexing model from the issue text.