Objective

#10644 introduced nice "statically typed" labels that replace the old strings. I would like to propose some changes to the names introduced:

• SubGraph2d -> Core2d and SubGraph3d -> Core3d. The names of these graphs have been / should continue to be the "core 2d" graph not the "sub graph 2d" graph. The crate is called bevy_core_pipeline, the modules are still core_2d and core_3d, etc.
• Labels2d and Labels3d, at the very least, should not be plural to follow naming conventions. A Label enum is not a "collection of labels", it is a specific Label. However I think Label2d and Label3d is significantly less clear than Node2d and Node3d, so I propose those changes here. I've done the same for LabelsPbr -> NodePbr and LabelsUi -> NodeUi

Additionally, #10644 accidentally made one of the Camera2dBundle constructors use the 3D graph instead of the 2D graph. I've fixed that here.

Changelog

• Renamed SubGraph2d -> Core2d, SubGraph3d -> Core3d, Labels2d -> Node2d, Labels3d -> Node3d, LabelsUi -> NodeUi, LabelsPbr -> NodePbr