Layout Builder field blocks show up on Block UI when they shouldn't

Removed the FieldBlock module mention from the summary. Tested it and it doesn't work this way.

Patch from @tim.plunkett's work

+++ b/core/modules/block/block.module
@@ -284,3 +284,25 @@ function block_configurable_language_delete(ConfigurableLanguageInterface $langu
+    // Filter out any definition with required contexts.
+    elseif (!empty($definition['context'])) {
+      /** @var \Drupal\Core\Plugin\Context\ContextDefinitionInterface $context */
+      foreach ($definition['context'] as $context) {
+        if ($context->isRequired()) {
+          unset($definitions[$id]);
+          break;
+        }
+      }

This seems to disruptive. Couldn't a contrib module provide to UI for providing contexts if needed or have some other logic for providing contexts to the block UI?

It seems likes we should only be removing layout builder provided blocks here and the Block module should implement this logic if needed.

Re #10

1. It would be nice to have a second implementation but since the layout builder also will opens block in dialog I think we still getting complex test scenario for the ajax if we switch to using layout builder. Also the block UI doesn't open up the configure link in the a dialog so Layout Builder case is more complex I think.
2. But if the patch was changed to my suggestion in #12 then quick way to test would be to create a test module that has empty block plugin class that extends \Drupal\layout_builder\Plugin\Block\ExtraFieldBlock with only the annotation id changed. That way they won't be removed and we could test the blocks plugins in the Block UI.

1. re #12 I change this to be in the layout_builder module and only unset where the provider is layout_builder
2. Added the test I suggested in #13.2 but it extends Drupal\layout_builder\Plugin\Block\FieldBlock not ExtraFieldBlock. That was a mistake. The test fails because of this error..
   

   The website encountered an unexpected error. Please try again later.Drupal\Core\Config\Schema\SchemaIncompleteException: Schema errors for block.block.datefield with the following errors: block.block.datefield:settings.formatter missing schema in Drupal\Core\Config\Development\ConfigSchemaChecker->onConfigSave() (line 95 of core/lib/Drupal/Core/Config/Development/ConfigSchemaChecker.php).

   call_user_func(Array, Object, 'config.save', Object) (Line: 111)

   I am not sure why. I don't see layout_builder setting this in the schema so not sure why the test module would be fail and the regular blocks module won't. Probably missing something simple.