when a script calls Processing.initialize() if they are not
already loaded
This means the following ugly code can be avoided:
Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms(QgsApplication.processingRegistry()))
QgsApplication.processingRegistry().addProvider(Qgs3DAlgorithms(QgsApplication.processingRegistry()))
and instead the call to Processing.initialize() is sufficient to load
ALL providers
Fixes#41310