refactor: use parserServices.getDocumentFragment

Author: tyankatsu0105

Diff for: lib/rules/no-empty-component-block.js

@@ -47,14 +47,11 @@ module.exports = {
    * @returns {RuleListener} AST event handlers.
    */
   create(context) {
+    const componentBlocks = context.parserServices.getDocumentFragment()
+      .children
+
     return {
       Program(node) {
-        if (!node.templateBody) {
-          return
-        }
-
-        const componentBlocks = node.templateBody.parent.children
-
         for (const componentBlock of componentBlocks) {
           if (
             componentBlock.name !== 'template' &&