QmlJS: Update QML parser using the one from qtdeclarative 5.15

We need to do this because the new "required" keyword should be
recognized by Qt Creator.

This is not a verbatim copy of the QML parser from qtdeclarative. A few
data structures have changed that would require large scale changes in
otherwise unrelated parts of the code. For example, all Visitors need to
handle recursion depth errors now and the DiagnosticMessage only has
line and column now, no longer begin and legth.

Change-Id: Iea5b04e27b07e0cba55d64b844315af9828acbf7
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/qmljs/parser/qmljsastvisitor.cpp

@@ -29,7 +29,7 @@ QT_QML_BEGIN_NAMESPACE
 
 namespace QmlJS { namespace AST {
 
-Visitor::Visitor()
+Visitor::Visitor(quint16 parentRecursionDepth) : m_recursionDepth(parentRecursionDepth)
 {
 }