Implement IDBVersionChangeEvent ctor w/ IDBVersionChangeEventInit dict

LayoutTests/storage/indexeddb/event-init-expected.txt

+Verify the use of IDBVersionChangeEventInit
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+event = new IDBVersionChangeEvent('default')
+PASS event instanceof IDBVersionChangeEvent is true
+PASS event.type is "default"
+PASS event.oldVersion is 0
+PASS event.newVersion is null
+
+initEvent = {oldVersion: 123, newVersion: 456}
+event = new IDBVersionChangeEvent('foo', initEvent)
+PASS event instanceof IDBVersionChangeEvent is true
+PASS event.type is "foo"
+PASS event.oldVersion is initEvent.oldVersion
+PASS event.newVersion is initEvent.newVersion
+
+initEvent = {oldVersion: 'legacy', newVersion: null}
+event = new IDBVersionChangeEvent('bar', initEvent)
+PASS event instanceof IDBVersionChangeEvent is true
+PASS event.type is "bar"
+PASS event.oldVersion is 0
+PASS event.newVersion is null
+PASS successfullyParsed is true
+
+TEST COMPLETE
+