The attribute-group and model-group redefine-restriction rules built the
namespaced base-component pool and did the namespaced-key-plus-chameleon-fallback
lookup with duplicated code and near-identical comments. Extract baseComponents(in:
named:) and resolveBaseComponent(_:name:owner:) so the recurring namespace-keying
and chameleon-fallback pattern lives in one place. Behavior-preserving: all redefine
unit tests pass and the XSTS buckets are unchanged (0/48/0/31).
Mihaela Mihaljevic
d046189ad6