Ensure global is present in top level

* Set `global` as part of initialisation.
* Add a test that `global` and `globalThis` are the same thing.

Author: aardvark179

rhino/src/main/java/org/mozilla/javascript/ScriptRuntime.java

@@ -190,6 +190,8 @@ public static ScriptableObject initSafeStandardObjects(
             ((TopLevel) scope).clearCache();
         }
 
+        scope.put("global", scope, scope);
+
         scope.associateValue(LIBRARY_SCOPE_KEY, scope);
         new ClassCache().associate(scope);
         new ConcurrentFactory().associate(scope);

tests/src/test/java/org/mozilla/javascript/tests/TopLevelTest.java

@@ -0,0 +1,7 @@
+package org.mozilla.javascript.tests;
+
+import org.mozilla.javascript.drivers.RhinoTest;
+import org.mozilla.javascript.drivers.ScriptTestsBase;
+
+@RhinoTest(value = "testsrc/jstests/top-level.js")
+public class TopLevelTest extends ScriptTestsBase {}

tests/testsrc/jstests/top-level.js

@@ -0,0 +1,7 @@
+'use strict';
+
+load("testsrc/assert.js");
+
+assertSame(global, globalThis);
+
+"success";