qmljs: update parser

Update the qtcreator qmljs parser to the
one of Qt 5.12. It supports EcmaScript 7.

Task-number: QTCREATORBUG-20341
Change-Id: I0d1cff71402ba17e22cde6b46c65614e162280de
Reviewed-by: Erik Verbruggen <erik.verbruggen@qt.io>

src/libs/qmljs/parser/qmljsengine_p.cpp

@@ -98,15 +98,8 @@ double integerFromString(const char *buf, int size, int radix)
     return result;
 }
 
-double integerFromString(const QString &str, int radix)
-{
-    QByteArray ba = QStringRef(&str).trimmed().toLatin1();
-    return integerFromString(ba.constData(), ba.size(), radix);
-}
-
-
 Engine::Engine()
-    : _lexer(0), _directives(0)
+    : _lexer(nullptr), _directives(nullptr)
 { }
 
 Engine::~Engine()