Class Node2D

A plain grouping container under an MWG-owned name, for the common "just group some children" need Scene2D.stage itself covers for the whole scene - a sub-layer inside it (a HUD strip, a creature layer, a popup stack) still needs its own constructible class. Container2D (Types2D.ts) is itself a value re-export of the same underlying class, so new Container2D() also works; Node2D exists as the name this module and its own doc comments actually use, so a game reads one name rather than two for the same thing.

A bare re-export under this name, deliberately: Pixi's own Container already does everything this needs, so the point is not to add behaviour but to give a game a name it can import without naming pixi.js itself.