Use combinedClickable as basis of UnboundedRippleButton

[kevinGC]

WHAT

Allow users of user of UnboundedRippleButton to use features like long press.

WHY

Long press is useful for UI interactions, e.g. for a button that skips forward 30 seconds upon clicking, and skips to the end when held.

HOW

Use combinedClickable instead of clickable.

Checklist 📋

• Add explicit visibility modifier and explicit return types for public declarations
• Run spotless check
• Run tests
• Update metalava's signature text files

[yschimke]

This isn't passing in any additional lambda, so not sure it's letting anyone pass this in.

[kevinGC]

Whoops, embarrassing omission. Updated, plus updated the relevant bit of the API file.