What does this PR do?

Allows Button as to accept elementType. This is important for cases when someone uses a router like react-router-dom and wants to do something like:

<Button
   as={Link}
   to="/home" (to is the prop for react-router-dom link)
   label="Home"
/>

Where should the reviewer start?

What testing has been done on this PR?

How should this be manually tested?

Do Jest tests follow these best practices?

• screen is used for querying.
• The correct query is used. (Refer to this list of queries)
• userEvent is used in place of fireEvent.
• asFragment() is used for snapshot testing.

Any background context you want to provide?

What are the relevant issues?

Screenshots (if appropriate)

Do the grommet docs need to be updated?

Should this PR be mentioned in the release notes?

Yes.

Is this change backwards compatible or is it a breaking change?

Backwards compatible.