Issue #3459246: Add a '#selectall' option for checkboxes element

Closes #3459246

core/config/schema/core.entity.schema.yml

@@ -248,6 +248,14 @@ field.widget.settings.boolean_checkbox:
       type: boolean
       label: 'Display label'
 
+field.widget.settings.options_buttons:
+  type: mapping
+  label: 'Check boxes/radio buttons format settings'
+  mapping:
+    check_all_enabled:
+      type: boolean
+      label: 'Check All enabled'
+
 field.widget.settings.hidden:
   type: mapping
   label: '- Hidden - format settings'