EntityDisplayBase::init() should use ::setComponent() for extra fields

The changes look good.
Looking at \Drupal\Core\Entity\EntityDisplayBase now the only instance of $this->content[$name] = is inside \Drupal\Core\Entity\EntityDisplayBase::setComponent()

And the only instance of $this->hidden[$name] = TRUE; is in \Drupal\Core\Entity\EntityDisplayBase::removeComponent()

RTBC, if patches test/fail as expected I think it is good.

Discussed with @tim.plunkett. He mentioned that this will result in changes to config exports as there are new entries added to entity displays for each field. So we need an upgrade path here to re-save the config so it happens on update rather than randomly adding diffs when something else is updated.

Per @tim.plunkett this is a blocker for #2953656: No ability to control "extra fields" with Layout Builder and the workaround without this fix is icky and possibly a performance issue. Layout Builder is beta experimental and so can have new BC functionality added in patch releases etc., so not having the issue affects how cleanly the fix can be backported to beta. However, since this is an issue with the entity system itself and upgrade paths that update config are preferably minor-only: I think we should start by getting this into 8.6.x, and then after commit we can decide whether it's better to backport this or not.

Thanks!

I was discussing this issue with Tim and I tried to use the existing test fixture locally and I can't seem to replicate the failures from #6. Let's try this out quickly, the interdiff is relative to the PASS patch from #6.

Looks great! Good tests!

duh!! Sorry about setting to RTBC in #10 when it actually needed a reroll. By the end of my review I had forgotten that had to reroll the patch for system.post_update.php

Sorry to drop this back to NW, but the comment needs work

1. +++ b/core/modules/field_ui/tests/src/Kernel/EntityDisplayTest.php
   @@ -166,7 +166,7 @@ public function testExtraFieldComponent() {
   -    $this->assertEqual($display->getComponent('display_extra_field'), ['weight' => 5, 'region' => 'content']);
   +    $this->assertEqual($display->getComponent('display_extra_field'), ['weight' => 5, 'region' => 'content', 'settings' => [], 'third_party_settings' => []]);
   

   could we split this array over multiple lines for readability? think it would fail phpcs as is

2. +++ b/core/modules/system/system.post_update.php
   @@ -139,3 +141,32 @@ function system_post_update_change_delete_action_plugins() {
   +    // If any extra fields have are used as a component, resave the display with
   +    // the updated component information.
   

   the english is off here

Fixes for #15

Crediting @xjm for the review that asked for an update path.

Not crediting my nit-review

Committed as 223216c and pushed to 8.6.x.

Leaving at RTBC and will discuss with @xjm re back-port question raised in #5