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."

Beginne damit, die vorhandenen Erscheinungsoptionen von matButton mit matIconButton zu vergleichen, und prüfe anschließend die im Issue verlinkten Icon-Button-Varianten von Material Design 3. Als abgeschlossen gilt die Arbeit, wenn matIconButton gefüllte und tonale Erscheinungsbilder als kreisförmige Icon-Buttons rendern kann, die sich von FABs und standardmäßigen Icon-Buttons unterscheiden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.