Prevent default when the submit button is clicked while isPending is true

[sookmax]

Closes #6197

I could've placed the logic in disablePendingProps, but thought it might be confusing for the user to see the warning message every time they click on the button while pending.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

Story

http://localhost:9003/?path=/story/button--pending-spinner&providerSwitcher-express=false&strict=true

form_submit_1080.mov

🧢 Your Project:

[snowystinger]

Thanks for the PR!

[snowystinger]

i think we can always prevent the default as I imagine we'd need to do it for type === 'reset' too.

Can you think of a reason we'd allow it?

I think this is a fine place for the check, we'll eventually move pending logic into RAC, so we can always reevaluate then.

[sookmax]

Thanks for the review!

Yeah I think it's safe to prevent default as long as the element is <button> since it makes sense to prevent the default behaviors for type=submit and type=reset, and type=button actually doesn't have a default behavior, it seems.