Calypsoify: Add support for switching to Classic when iframing the block editor.

[kwight]

When using WordPress.com to edit a WordPress.com site, we give a menu option in the block editor to easily switch to the Calypso editor. With upcoming support for editing Jetpack sites with the block editor on WordPress.com, this PR will give the same option for Jetpack users.

Note that the changes to modules/calypsoify/class.jetpack-calypsoify.php could have been a little simpler, but these changes bring it more in line with the Calypsoify class active on WP.com; knowing we'll be faced with bringing the two more in sync in the future, keeping them as similar as possible for now seems the prudent approach.

Testing instructions:

• Load http://calypso.localhost:3000/block-editor/post/:JPsite (JPSite being your test site with this Jetpack repo installed).
• Verify the block editor ellipsis menu does not have the "Switch to Classic Editor" item.
• Switch your Jetpack plugin to this branch.
• Reload http://calypso.localhost:3000/block-editor/post/:JPsite.
• Verify the block editor ellipsis menu does have the "Switch to Classic Editor" item.

Proposed changelog entry for your changes:

• N/A

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: May 7, 2019.
Scheduled code freeze: April 30, 2019

Generated by 🚫 dangerJS against 92ac7fe

[mmtr]

Awesome, this worked wonderfully for me!

Note that I had to use a different browser to test, because my usual browser was loading a cached version of the wpcom-block-editor/common.js script don't including the required latest changes we added earlier this week in Automattic/wp-calypso#32421 / D27149-code.

[jeherve]

This should need a rebase now.

[kwight]

Rebased and ready to go again – thanks @jeherve ! 👍

[jeherve]

This worked well in my tests. I only had 2 comments, that may not be blocking. I'll let you judge.