Component-scoped configuration cascade for the tag family. Pass
any combination of feature factories in a parent component's
viewProviders array.
Unlike provideTagConfig (root-only), provideTagConfigAt injects
the parent injector's CNGX_TAG_CONFIG value (resolves through
the priority chain — root provider, library defaults, or another
provideTagConfigAt further up) and deep-merges the supplied
features on top. This produces cumulative cascade behaviour:
descendant tag instances see the merged config, sibling sub-trees
keep the inherited value untouched.