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?

Verwende die verknüpfte StackBlitz-Reproduktion, beginne mit src/app/example-component.html und schalte die Checkbox um, um das deaktivierte Input und den Suffix zu vergleichen. Verfolge das Styling des mat-form-field-Suffix und überprüfe, dass der Suffix mit der Schriftstärke, Farbe und Deckkraft des deaktivierten Inputs übereinstimmt, während das Verhalten für nicht deaktivierte Elemente erhalten bleibt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.