Stop using module.createRequire (problematic under webpack), incorporate and export resolveModule helper from markdownlint-cli2.

test/rules/node_modules/markdownlint-rule-sample-module/sample-rule.mjs

@@ -0,0 +1,18 @@
+// @ts-check
+
+const rule = {
+  "names": [ "sample-rule-module" ],
+  "description": "Sample rule (module)",
+  "tags": [ "sample" ],
+  "function": (params, onError) => {
+    const hrTokens = params.tokens.filter((token) => token.type === "hr");
+    for (const token of hrTokens) {
+      onError({
+        "lineNumber": token.lineNumber,
+        "detail": "Sample error for hr"
+      });
+    }
+  }
+};
+
+export default rule;