List Niagara Emitters

Emitters in a Niagara system, with the settings_prefix that makes them editable. An emitter's settings live inside VersionData[N] on the emitter object, so a property path without that prefix resolves to nothing. Combine emitter_object and settings_prefix for hf_get_property and hf_set_property, as in VersionData[0].bLocalSpace.