Previously, the SW was only able to clean up caches for app-versions
found in the `Driver`'s `versions` map. If (for some reason) the
`Driver` failed to load a valid stored state (including app-versions)
and ended up with an [empty `versions` map][1], any obsolete versions
would remain in the cache storage. This case was rare but possible.
This commit makes the cache clean-up logic more robust by ensuring that
all app-version caches are removed unless they are currently used by the
SW to serve active clients (with the exception of the latest
app-version, which is always retained).
Fixes #41728
[1]: 9de65dbdce/packages/service-worker/worker/src/driver.ts (L515-L529)
PR Close #42622