feat(button): add filled/tonal matIconButton

### Feature Description

Currently, matButton supports multiple appearances (text, filled, tonal, outlined, elevated) via the matButton attribute, but matIconButton does not accept any appearance input — it always renders as a transparent circular button.

Material Design 3 specifies [filled and tonal icon button variants](https://m3.material.io/components/icon-buttons/overview) as distinct components alongside the standard and outlined icon buttons. There is currently no straightforward way to create these in Angular Material without using matFab/matMiniFab (which have different sizing, elevation, and semantics) or matButton="filled" with an icon (which doesn't produce a circular icon button).

### Use Case

Developers building M3-compliant UIs need filled and tonal icon buttons for actions that require more visual emphasis than a standard icon button, but don't carry the semantic meaning of a FAB (floating action button). For example, a filled icon button for a primary action like "play" or "add to cart" in a toolbar, or a tonal icon button for a medium-emphasis toggle like "bookmark" or "favorite."

Inizia confrontando le opzioni di aspetto esistenti di matButton con matIconButton, quindi esamina le varianti dei pulsanti icona di Material Design 3 collegate nell’issue. Il lavoro è completato quando matIconButton può eseguire il rendering di aspetti filled e tonal come pulsanti icona circolari, distinti dai FABs e dai pulsanti icona standard.

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