Add oEmbed optimizer module

[adamsilverstein]

Summary

Full issue - #888

Attempts to optimize oEmbeds using two techniques:

• For oEmbeds delivered as iframes, ensure the loading=lazy attribute is present
• For oEmbeds built using script tags:
  • move the script src to a data attribute
  • add a page level interaction observer that resets src before the user scrolls to the oEmbed

Related: https://core.trac.wordpress.org/ticket/58773

Relevant technical choices

Checklist

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[sgomes]

Thank you for the PR, @adamsilverstein! I think this has the potential for some great wins! 👍

I left some non-blocking comments for your consideration. I'm not sure if I'll have the opportunity to re-review because of some upcoming AFK, so please feel free to move ahead at your discretion!

[adamsilverstein]

Thanks for all the feedback and suggestions @westonruter and @mukeshpanchal27! I'm going to work on adding tests.

[westonruter]

Two things:

1. Shouldn't tests be added prior to merging?
2. No new modules have been merged in a while as they're waiting for migration to standalone plugins. I don't think we're supposed to be adding new modules.

Perhaps what should be done is to create a new feature/lazy-embeds branch off of trunk and then re-base this PR to target it. Then it can be merged prior to tests and we can also wait until we have the module-to-plugins plumbing finished.

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[adamsilverstein]

Perhaps what should be done is to create a new feature/lazy-embeds branch off of trunk and then re-base this PR to target it. Then it can be merged prior to tests and we can also wait until we have the module-to-plugins plumbing finished.

That sounds good to me!

[westonruter]

I created the feature/lazy-embeds branch but I can't change the base branch in your PR since it is on a fork. You'll have to do that. Once you've done it we can merge and then proceed with tests.

[adamsilverstein]

I created the feature/lazy-embeds branch but I can't change the base branch in your PR since it is on a fork. You'll have to do that. Once you've done it we can merge and then proceed with tests.

Thanks @westonruter - changed base branch