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

Comienza con la sección afectada «Customizing Your Typography» de la guía de theming y compárala con la guía de migración de Material 2 enlazada en el issue. Documenta cómo se puede personalizar la tipografía de Material 3, incluido el enfoque de configuración de Sass mostrado en el informe, y asegúrate de que la página responda a la pregunta sobre la personalización en lugar de limitarse a describir el uso.

Escrito por el modelo de indexación a partir del texto del issue.