Refactor: Load ETK common code before the plugins_loaded action

[p-jackson]

Changes proposed in this Pull Request

common/index.php contains helper functions that would be useful when other ETK modules are being setup during the plugins_loaded action. Unfortunately they can't be used though, because those helper functions are defined as part of plugins_loaded too.

There's nothing in common/index.php that means loading it should be delayed. So moving the require_once call so that it gets loaded as soon as full-site-editing-plugin.php is loaded.

Context: as part of #51122 I want to be able to call get_iso_639_locale() during Starter_Page_Templates's __construct(), so I want to guarantee that get_iso_639_locale() gets defined first.

Testing instructions

• install-plugin.php etk update/etk-load-common-code-earlier
• Smoke test ETK, it's functions should still load (new page modal, launch flows, etc.)
• Verify that the common js/css assets are still enqueued (e.g. check for hide-plugin-buttons-mobile.css in the network tab)

[matticbot]

Test live: https://calypso.live/?branch=update/etk-load-common-code-earlier

[noahtallen]

This makes perfect sense to me, and it tests well. It doesn't really make a difference on JS/CSS loading order either, since those still use normal hooks.

[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.

[p-jackson]

😎 thanks @noahtallen
I thought you might have been interested in this from a workflow point of view. This got a fast review so probably won't matter now, but having two PRs, where the second one's branch is based off the first one, is a way we can make this sort of things easily testable. Using install-plugin.php on the second PR will allow us to test the whole feature together like we generally do when making wpcom changes.

[noahtallen]

Using install-plugin.php on the second PR will allow us to test the whole feature together like we generally do when making wpcom changes.

That's super cool, I don't think I'd considered that workflow. But it's really nice that it works 😎

[autumnfjeld]

@p-jackson Just a lil heads up that it's install-plugin.sh not install-plugin.php. 😄 Took me a bit of what-am-i-doing-wrong and searching when I did a previous review with that also had the erroneous .php extension.