Elements: Add a more usable API

[scruffian]

What problem does this address?

We introduced a class name for button elements in #40260, but to use this developers need to look up what the correct class name for each element is which is far from ideal.

What is your proposed solution?

There was some discussion in #40260 about the best way forward but we didn't reach any agreement, here are some options:

1. Each element could have a component
2. We could have a hook that adds the class name to the block props
3. We could have a simple function that returns the correct class name when passed an element name.

For what it's worth, my preference is option 3.

[scruffian]

Fixed by #41753