Editing Toolkit: Update to 2.8.4

[ciampo]

Changes proposed in this Pull Request

• Version bump and changelog

Changes to Editing Toolkit since 2.8.3:

• Editor NUX modal: Temporarily make text smaller in editor welcome modal for german language (Editor NUX modal: Temporarily make text smaller in editor welcome modal for german language #47193)
• Editor Toolkit: update slide copy in NUX (Editor Toolkit: update slide copy in NUX #46674)
• Focused Launch: fix domain picker not showing in summary page in Calypso (Focused Launch: fix domain picker not showing in summary page in Calypso #47141)
• Reinstating condition (Editing Toolkit: set translations for NUX modal #47136)
• Make text of Premium Content's Subscribe button editable (Make text of Premium Content's Subscribe button editable #46983)
• Remove premium content block placeholder. (Premium Content: Remove premium content block placeholder #47068)
• Focused Launch: use site title hook in the name step (Focused Launch: use site title hook in the name step #46921)
• Add block pattern dom validation tests (Add block pattern dom validation tests #45747)
• For the coming soon fallback page: namespace the class names, add an svg for the wp logo (Coming Soon: updating the fallback page #46994)
• Remove unused vars (Remove unused vars from global styles font pairings #47072)
• Update global font pairings (Update global font pairings #46927)
• Add recordTracksEvent for Editor NUX modal (Add recordTracksEvent for Editor NUX modal #46796)

Testing instructions

1. Load the diff on your sandbox D52369-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=update/edt-2.8.4

[matticbot]

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

D52369-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.

[ciampo]

It looks like the text in the last slide of the editor welcome modal is not translated correctly:

See p1604665886075900-slack-C014TPFLP for more details.

We should:

• wait for Editor NUX modal: Temporarily make text smaller in editor welcome modal for german language #47193 to be merged merged
• wait for the translations to be picked up apparently, in order for translations to appear, we need to release the plugin to .org first — which means that potentially some user will see the untranslated text
• rebase on top of master, and update this PR to include all of the changes that were committed to Editing Toolkit in the meantime no changes to apps/editing-toolkit since last rebase
• re-test changes and deploy

[autumnfjeld]

Verified:
✅ Add recordTracksEvent for Editor NUX modal (#46796) : track events are firing and sending network request

[ciampo]

D52369-code deployed, 2.8.4 released to dotorg. I'm going to merge this PR too

The failing phpunit test is caused by a mismatch in the node version — see p1604598992424000-slack-C02DQP0FP