feat(core): Expose SCSS breakpoints

### Feature Description

As @angular/flex-layout become deprecated and Angular team does not intend to provide an alternative, we are forced to handle responsive layout by our own.

Writing CSS is ok, but to stick with Material design guidance we must use specific breakpoints. It would be great if @angular/material could expose these breakpoints like it does for palettes and theming. Otherwise we have to declare them ourself for every projects.

### Use Case

would simplify scss writting and add opinions about breakpoints (like CDK Layout API)

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

@media #{$mat.gt-xs} {
// insert your styles
}
```

Comienza comparando las variables de breakpoint de SCSS solicitadas con la CDK Layout API y la superficie de theming de Angular Material mencionadas en el issue. Se considera completado cuando Angular Material expone valores de breakpoint documentados que se pueden consumir en media queries de SCSS sin redefinirlos en cada proyecto.

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