RELNOTES[NEW]: Add goog.string.Unicode.ZERO_WIDTH_SPACE.

This is useful for word-wrapping in text context (same as <wbr> in HTML context). Zero-width space is an invisible character so it's better to use it in the code indirectly through this enum.

PiperOrigin-RevId: 473309362
Change-Id: Ia8ab342d28d09af1317875da508f7e4b304f09bf

closure/goog/string/string.js

@@ -41,7 +41,8 @@ goog.string.FORCE_NON_DOM_HTML_UNESCAPING =
  * @enum {string}
  */
 goog.string.Unicode = {
-  NBSP: '\xa0'
+  NBSP: '\xa0',
+  ZERO_WIDTH_SPACE: '\u200b'  // This is equivalent to <wbr>.
 };