feat(material/button): add support for tonal button

[crisbeto]

Adds support for the tonal button appearance from the spec. It can be enabled by setting matButton="tonal" on the button.

Fixes #28809.

[github-actions]

Deployed dev-app for 5693a07 to: https://ng-dev-previews-comp--pr-angular-components-30638-dev-8rktwxmd.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

[eneajaho]

Looks like density is not being applied.

[crisbeto]

oops, good catch. I've pushed a fix.

[JWess]

Why does it use matButton="tonal" instead of mat-tonal-button, a la mat-stroked-button, mat-raised-button, and mat-flat-button?

[mjamin]

Looks like an oversight not to include 'tonal' in the selectors and _inferAppearance?

[JWess]

@crisbeto Any word on the two questions above?

[crisbeto]

I intentionally didn't include an attribute selector for the tonal button, because long-term we want to switch to the matButton input. It has the advantage of being type-checked and supporting dynamic changes of the appearance.

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