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."

Start by comparing the existing matButton appearance options with matIconButton, then review the Material Design 3 icon-button variants linked in the issue. Done means matIconButton can render filled and tonal appearances as circular icon buttons, distinct from FABs and standard icon buttons.

Written by the indexing model from the issue text.