Contact Form AMP Support

[jeffersonrabb]

The Contact Form block's date picker enqueues several scripts, which causes the block to break in AMP environments.

Changes proposed in this Pull Request:

• This PR uses the amp-date-picker element (https://amp.dev/documentation/components/amp-date-picker) making the Contact Form block fully AMP compatible.

Testing instructions:

• Spin up a new Jurassic Ninja instance using this URL: https://jurassic.ninja/create/?jetpack-beta&branch=add/amp-contact-form
• Connect Jetpack
• Install and activate the AMP plugin: https://wordpress.org/plugins/amp/.
• Go to the AMP settings page (/wp-admin/admin.php?page=amp-options) and switch mode to Transitional.
• Create a new post and insert the Form block, and set it up to send to an email you receive.
• Add a Date Picker form element to the form.
• Publish or preview the post, and submit the form.
• Switch to AMP version (either use admin nav to toggle or simply add ?amp to the end of the URL).
• Submit the form.
• Verify that form submission works correctly in AMP and non-AMP environments, and that date picker value is included in both.
• Observe the date picker UI looks different in AMP version:

Proposed changelog entry for your changes:

• Contact Form block AMP compatibility.

[jetpackbot]

	Warnings
⚠️	The PR is missing at least one [Status] label. Suggestions: [Status] In Progress, [Status] Needs Review

This is an automated check which relies on PULL_REQUEST_TEMPLATE. We encourage you to follow that template as it helps Jetpack maintainers do their job. If you think 'Testing instructions' or 'Proposed changelog entry' are not needed for your PR - please explain why you think so. Thanks for cooperation 🤖

Generated by 🚫 dangerJS against 43ea931

[westonruter]

Part of #9730. Will ✅ this:

[jeherve]

This works well for me, although there are some layout issues with the AMP date picker right now: