Issue #3456024 Tree validation

Closes #3456024

config/schema/experience_builder.schema.yml

@@ -78,10 +78,14 @@ experience_builder.component.*:
                 # @todo Add `StructuredDataPropExpression` validation constraint that fails if StructuredDataPropExpression::fromString() fails
                 # StructuredDataPropExpression: [field_type]
 
-# @todo reuse the yet-to-be-written validation logic that \Drupal\experience_builder\Plugin\Field\FieldType\ComponentTreeItem::preSave() is referring to
-field.value.component_tree:
-  type: field.value.*
-  label: 'Default value'
+# The config equivalent of a ComponentTreeItem, validated by the same constraint.
+# @todo Use this in https://www.drupal.org/project/experience_builder/issues/3455629
+experience_builder.component_tree:
+  type: mapping
+  label: 'Config-Defined Component Tree'
+  constraints:
+    ValidComponentTree: ~
+    FullyValidatable: ~
   # @see \Drupal\experience_builder\Plugin\Field\FieldType\ComponentTreeItem::propertyDefinitions()
   mapping:
     # @see \Drupal\experience_builder\Plugin\DataType\ComponentTreeStructure
@@ -93,6 +97,12 @@ field.value.component_tree:
       type: string
       label: 'Prop values for each component in the component tree'
 
+field.value.component_tree:
+  type: experience_builder.component_tree
+  label: 'Default value'
+  constraints:
+    FullyValidatable: ~
+
 field.field_settings.component_tree:
   type: field.field_settings.*
   constraints: