addBuilder
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.
Parameters
builder
the builder to register.