Fixes#25018.
Instantiating a NgModuleRef from NgModuleFactory reuses the NgModuleDefinition if it is already present. However the NgModuleDefinition has a providers array which modified when tree shakable providers are instantiated. This corrupts the provider definitions the next time the same factory is used to create a new NgModuleRef - Two provider definitions can end up with the same index anf the injector could potentially return a completely wrong object for a provider token.
This scenario is more likely on the server where the same NgModuleFactory is reused across requests.
The fix clones the cached NgModuleDefinition so that any tree shakable providers added later do not affect the cached copy.
PR Close#25022
This allows to overwrite templates for JIT and AOT components alike.
In contrast to `TestBed.overrideTemplate`, the template is compiled
in the context of the testing module, allowing to use other testing
directives.
Closes#19815
