feat(theming): Mixins for reading component style tokens

### Feature Description

Mixins to get values from a component theme that takes a token as parameter, for example:
```
p {
color: @include mat.button-get(text-label-text-color);
}
```
it would generate:
```
p {
color: var(--mdc-outlined-button-label-text-color, var(--mat-sys-primary)); // <== Actual value used for text-button
}
```

Ideally, we would have as many mixins as there are components (+core) and we could use the same tokens as the `mat.-overrides` mixins.

> The `mat.-get` mixin name is a proposal, open to suggestions.

### Use Case

I have a custom component and I want to apply the same style as a material component. I also want to make sure that they are always in sync when I change my theme.

For example, I want to have a text `

` with the same font color as my `mat-button` next to it.

For now, I need to rely on private CSS variables to do that, which is not ideal for maintainability.

La issue non indica file o test. Inizia leggendo i mixin `mat.-overrides` esistenti e confrontando i relativi token con l’API `mat.-get` proposta. Il lavoro sarà completo quando saranno definiti l’ambito desiderato del mixin e la relativa denominazione, e gli utenti potranno leggere i valori dei token del tema dei componenti per gli stili personalizzati.

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