Background
Following IParticleSystem: add doNotSerialize, ISpriteManager and impls have no doNotSerialize to control if a sprite manager should be serialized.
Proposal
Add an optional doNotSerialize to ISpriteManager, and impl it in SpriteManager with a default false, so existing code would not be broken, and since it’s optional, compatiblity is preserved for typescript users making their own impls.
In SceneSerializer._Serialize, doNotSerialize would be checked like all other type of objects for ISpriteManagers.
