dumpccp wrongly use a private qmetatype interface

Dumpcpp tool uses an explicit template specialization to insert own code to meta - type system. The problem is that the code doesn't meet requirements of the QMetaType. It creates not fully functional helper functions that can asserts. Affected functions:

qMetaTypeDeleteHelper, qMetaTypeCreateHelper, qMetaTypeDestructHelper, qMetaTypeConstructHelper

or

class QMetaTypeFunctionHelper (after merge of https://codereview.qt-project.org/#change,35353)

Related change and discussion: https://codereview.qt-project.org/#change,35360