bug(mat-form-field): suffix element style should reflect input disabled state

### Reproduction

[Open this StackBlitz](https://stackblitz.com/edit/components-issue-8gvvrn?file=src/app/example-component.html) and toggle the Disabled state with the checkbox.

### Expected Behavior

Per [the Text Field spec](https://material.io/components/text-fields#outlined-text-field), under "Outlined text field with suffix text", a suffix in a disabled text field should use the same font (weight / color / opacity) as the wrapped input element.


(In the image from the spec, "55" is the input text and "/100" is the suffix.)

### Actual Behavior

The input text is light gray, to indicate that the input is disabled, but the suffix styling does not change, so it doesn't match the input text.

### Environment

- Angular: 11.1
- CDK/Material: 11.1
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

### Note

I also see that in all the suffix examples where the input is *not* disabled, the suffix is styled slightly lighter than the input text. As you can see in the StackBlitz, the default suffix is exactly the same as the input text. The spec doesn't explicitly require this, as far as I can see, so maybe it's just a suggestion?

Usa la riproduzione StackBlitz collegata, iniziando da src/app/example-component.html, e attiva o disattiva la casella di controllo per confrontare l’input disabilitato e il suffisso. Traccia lo stile del suffisso di mat-form-field e verifica che il suffisso corrisponda al peso del carattere, al colore e all’opacità dell’input disabilitato, preservando al contempo il comportamento quando non è disabilitato.

Scritto dal modello di indicizzazione a partire dal testo della issue.