docs-bug(Typography): It isn't clear how to customise Material 3 typography

### Documentation Feedback

Material 2 docs were pretty clear about how to customise typography.

```
@use '@angular/material' as mat;

$my-custom-level: mat.m2-define-typography-level(
$font-family: Roboto,
$font-weight: 400,
$font-size: 1rem,
$line-height: 1,
$letter-spacing: normal,
);

$my-custom-typography-config: mat.m2-define-typography-config(
$headline-1: mat.m2-define-typography-level(112px, 112px, 300, $letter-spacing: -0.05em),
$headline-2: mat.m2-define-typography-level(56px, 56px, 400, $letter-spacing: -0.02em),
$headline-3: mat.m2-define-typography-level(45px, 48px, 400, $letter-spacing: -0.005em),
$headline-4: mat.m2-define-typography-level(34px, 40px, 400),
$headline-5: mat.m2-define-typography-level(24px, 32px, 400),
// ...
);
```

The current page called "Customizing Typography" doesn't have an information on how to customise it at all. It describes the usage only.

Migration guide isn't answering this question as well (https://material.angular.io/guide/material-2-theming#how-to-migrate-an-app-from-material-2-to-material-3).

### Affected documentation page

https://material.angular.io/guide/theming#customizing-your-typography

Inizia con la sezione interessata «Customizing Your Typography» della guida al theming e confrontala con la guida alla migrazione a Material 2 collegata nell’issue. Documenta come è possibile personalizzare la tipografia di Material 3, incluso l’approccio alla configurazione Sass mostrato nel report, e assicurati che la pagina risponda alla domanda sulla personalizzazione invece di limitarsi a descrivere l’utilizzo.

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