Refactor Token.parent() to Token.parent, add validation tests for parent, fix parent in htmlFlow scenario, improve type saftey slightly.

test/markdownlint-test-custom-rules.js

@@ -1489,7 +1489,11 @@ test("customRulesParamsAreFrozen", (t) => {
               t.true(Object.isFrozen(current) || (current === params));
               for (const name of Object.getOwnPropertyNames(current)) {
                 const value = current[name];
-                if (value && (typeof value === "object")) {
+                if (
+                  value &&
+                  (typeof value === "object") &&
+                  (name !== "parent")
+                ) {
                   pending.push(value);
                 }
               }

test/markdownlint-test-micromark.mjs

@@ -17,9 +17,26 @@ const testTokens = new Promise((resolve, reject) => {
   testContent.then(parse).then(resolve, reject);
 });
 
+const cloneToken = (token) => {
+  for (const child of token.children) {
+    const expectedParent = (token.type ? token : null);
+    if (child.parent !== expectedParent) {
+      throw new Error("Unexpected parent.");
+    }
+  }
+  const clone = { ...token };
+  delete clone.parent;
+  clone.children = clone.children.map(cloneToken);
+  return clone;
+};
+
+const cloneTokens = (tokens) => (
+  cloneToken({ "children": tokens }).children
+);
+
 test("parse", async(t) => {
   t.plan(1);
-  t.snapshot(await testTokens, "Unexpected tokens");
+  t.snapshot(cloneTokens(await testTokens), "Unexpected tokens");
 });
 
 test("getMicromarkEvents/filterByPredicate", async(t) => {