fix(donate-block): allow spaces in button label

[dkoo]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Fixes a minor but annoying bug in which the RichText component for the submit button in the editor for Donate blocks doesn't allow spaces if it's nested inside a button element. This fix changes the button element to a div with the same styles, in the editor only. See also Automattic/newspack-newsletters#1202

Closes 1204751246381643/1204483195828260.

How to test the changes in this Pull Request:

1. On master, add a Donate block to a post or page.
2. In both Frequency and Tiers layout options, observe that you can edit the submit button labels but can't add spaces in either case.
3. Check out this branch, repeat step 2 and confirm that you can now add spaces, and that both editor and front-end styles and behavior are otherwise unchanged.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[leogermani]

The changes work fine in the front-end but it broke the layout of the button for me in the editor

There's an extra padding and and a border

[dkoo]

Whoops, I got too fancy trying to inherit existing styles using an existing class name. But that class name has different styles depending on the "style" selected for the block. 250115f should make things consistent across all styles and layouts.

[matticbot]

🎉 This PR is included in version 1.71.0-alpha.1 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 1.72.0-alpha.1 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 1.72.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀