build: properly add pure annotations with tslib

Recently with angular#4787 the tsc generated helpers got replaced with helpers from the `tslib` package.

This means that the generated IIFE statements are different than before and the pure annotations RegExps don't work anymore.

Author: devversion

tools/gulp/packaging/pure-annotations.ts

@@ -7,7 +7,7 @@ const classIfeeRegex =
 
 /** Regex that matches downleveled class IIFE expressions with _extends statements */
 const classExtendsIfeeRegex =
-  /^(var (\S+) = )(\(function \(_super\) \{[\n\r]*    __extends\(\2, _super\);[\n\r]*)/gm;
+  /^(var (\S+) = )(\(function \(_super\) {[\n\r]*    tslib.*\.__extends\(\2, _super\);[\n\r]*)/gm;
 
 /**
  * Adds `@__PURE__` annotation comments to IIFEs containing ES5-downleveled classes generated by