[edalzell]

With a dedicated static_cache store, static:clear wiped the whole store but content saves under rules: all didn't, because DefaultInvalidator calls ApplicationCacher::flush() directly and that only walks the URL index.

The cachers now wipe the store themselves at the end of flush(), when their repository is the static_cache store, so both paths behave the same. The manager keeps its wipe for the null strategy and StaticCache::extend() drivers.

Closes #15860