Add overflow buttons to Twitter, Facebook, and Instagram embeds

[westonruter]

Summary

As of ampproject/amphtml#35027, Bento versions of amp-twitter, amp-facebook-*, and amp-instagram will require an overflow button to resize if they are in the initial viewport. This is to prevent these components from negatively impacting CLS, as they do currently. To prevent the need for users to click the overflow button, we'll eventually need to provide the components the required dimensions up-front as much as possible. See #4729.

Checklist

• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[github-actions]

Plugin builds for 294628a are ready 🛎️!

• Download development build
• Download production build

[delawski]

QA Passed

When embedding a Facebook post, an overflow button is added to the markup (it's not visible on the page itself):

Tested on AMP Version 2.2.0-alpha-20211123T020732Z-5405daa

[delawski]

I did another round of QA using the instructions shared by @westonruter on #6504 (comment).

Bento versions of amp-facebook, amp-instagram, and amp-twitter (as per #6504) display the "See more" button if placed "above the fold":

Initial embed	Expanded embed