NavigationBarItemSchemaBuilderScope

Registers builder as a child of this scope, snapshotting the CompositionLocal values currently active (via BuildContext.get) into GenericBuilder.compositionLocals — captured now, at DSL-call time, not later when build actually invokes it. Called once per nested DSL call (SimpleText(...), SendNetworkRequest(...), etc.) by each such call's own top-level builder function.

Builds every registered Builder in registration order, restoring each one's own GenericBuilder.compositionLocals snapshot (via BuildContext.with) for the duration of its own GenericBuilder.build call.

Declares one entry of a NavigationBar.