Tracepoints don't work in namespaced builds

As per subject.

The bug is twofold: for every tracepoint we generate a TRACEPOINT_EVENT and some function calls implementing the Qt-agnostic tracepoint calling.

1) The Qt-like parameters in TRACEPOINT_EVENT need QT_PREPEND_NAMESPACE wrapping, or they won't be found
2) The function calls are declared inside namespace QtPrivate, but that needs QT_BEGIN_NAMESPACE/QT_END_NAMESPACE wrapping

(TBH I'd also move them out of QtPrivate and into further sub-namespace)