Editing Toolkit: Update to 2.8.10

[stacimc]

Changes proposed in this Pull Request

• Bumps version of Editing Toolkit to 2.8.10

Changes included in this release

• Premium Content: Fix selection of payment plans (Correctly sync planId between PremiumContent and Payments block #47944)
• Coming Soon: Check for coming soon mode on 404 (Coming Soon: check for coming soon mode on 404 #47945)
• Onboarding: Add support for RTL site launch stylesheet (Onboarding: Add support for RTL site launch stylesheet to ETK #47890)
• Update to node 12.19.1 (Update to node 12.19.1 #47866)
• Coming soon: Show Coming Soon on blog post pages (Coming Soon: show Coming Soon page on blog post pages #47853)

Testing instructions

1. Load the diff on your sandbox (D53662-code) and confirm that the above changes work correctly
2. Test that the new version of the plugin doesn't break Atomic sites by following the instructions in the "Atomic Testing" section at PCYsg-ly5-p2.

[matticbot]

Test live: https://calypso.live/?branch=release/etk-2.8.10

[matticbot]

Caution: This PR affects files in the Editing Toolkit Plugin on WordPress.com
Please ensure your changes work on WordPress.com before merging.

D53662-code has been created so you can easily test it on your sandbox. See this FieldGuide page about developing the Editing Toolkit Plugin for more info: PCYsg-ly5-p2

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[noahtallen]

btw, the phpunit failure is expected, unfortunately.

Otherwise, I don't think the NodeJS upgrade should affect much 👍

[apeatling]

I've tested all the changes here, and they work fine on simple sites. Checking Atomic.

[apeatling]

Confirmed on Atomic sites too.

[p-jackson]

I've tested that Ramon and my changes are included and working on Atomic and Simple.