refactor(utils): remove duplicated function (#9972)

Co-authored-by: sebastien <lorber.sebastien@gmail.com>

packages/docusaurus-utils-common/src/stringUtils.ts

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/** Adds a given string prefix to `str`. */
+export function addPrefix(str: string, prefix: string): string {
+  return str.startsWith(prefix) ? str : `${prefix}${str}`;
+}
+
+/** Removes a given string suffix from `str`. */
+export function removeSuffix(str: string, suffix: string): string {
+  if (suffix === '') {
+    // str.slice(0, 0) is ""
+    return str;
+  }
+  return str.endsWith(suffix) ? str.slice(0, -suffix.length) : str;
+}
+
+/** Adds a given string suffix to `str`. */
+export function addSuffix(str: string, suffix: string): string {
+  return str.endsWith(suffix) ? str : `${str}${suffix}`;
+}
+
+/** Removes a given string prefix from `str`. */
+export function removePrefix(str: string, prefix: string): string {
+  return str.startsWith(prefix) ? str.slice(prefix.length) : str;
+}