chore: Make startsWith faster (#6118)

by using built-in function (polyfill will handle IE).

core/utils/parsing.js

@@ -15,7 +15,6 @@
 goog.module('Blockly.utils.parsing');
 
 const colourUtils = goog.require('Blockly.utils.colour');
-const stringUtils = goog.require('Blockly.utils.string');
 const {Msg} = goog.require('Blockly.Msg');
 
 
@@ -97,9 +96,8 @@ const tokenizeInterpolationInternal = function(
           // BKY_ is the prefix used to namespace the strings used in Blockly
           // core files and the predefined blocks in ../blocks/.
           // These strings are defined in ../msgs/ files.
-          const bklyKey = stringUtils.startsWith(keyUpper, 'BKY_') ?
-              keyUpper.substring(4) :
-              null;
+          const bklyKey =
+              keyUpper.startsWith('BKY_') ? keyUpper.substring(4) : null;
           if (bklyKey && bklyKey in Msg) {
             const rawValue = Msg[bklyKey];
             if (typeof rawValue === 'string') {

core/utils/string.js

@@ -19,17 +19,22 @@
  */
 goog.module('Blockly.utils.string');
 
+const deprecation = goog.require('Blockly.utils.deprecation');
+
 
 /**
- * Fast prefix-checker.
- * Copied from Closure's goog.string.startsWith.
+ * Obsolete prefix-checker.
  * @param {string} str The string to check.
  * @param {string} prefix A string to look for at the start of `str`.
  * @return {boolean} True if `str` begins with `prefix`.
  * @alias Blockly.utils.string.startsWith
+ * @deprecated April 2022. Use built-in string.startsWith.
  */
 const startsWith = function(str, prefix) {
-  return str.lastIndexOf(prefix, 0) === 0;
+  deprecation.warn(
+      'Blockly.utils.string.startsWith()', 'April 2022', 'April 2023',
+      'Use built-in string.startsWith');
+  return str.startsWith(prefix);
 };
 exports.startsWith = startsWith;