resourceloader: Migrate from msg_resource table to object cache

resourceloader: Migrate from msg_resource table to object cache

MessageBlobStore class:
* Make logger aware.
* Log an error if json encoding fails.
* Stop using the DB table. WANObjectCache supports everything we need:
  - Batch retrieval.
  - Invalidate keys with wildcard selects or cascading check keys.
* Update tests slightly since the actual update now happens on-demand as
  part of get() instead of within updateMessage().

ResourceLoader class:
* Remove all interaction with the msg_resource table. Remove db table later.
* Refactor code to use a hash of the blob instead of a timestamp.
  Timestamps are unreliable and roll over too frequently for message blob store
  because there is no authoritative source. The timestamps were inferred based on
  when a change is observed. Message overrides from the local wiki have an
  explicit update event when the page is edited. All other messages, such as
  from MediaWiki core and extensions using LocalisationCache, have a single
  timestamp for all messages which rolls over every time the cache is rebuilt.
  A hash is deterministic, and won't cause needless invalidation (T102578).
* Remove redundant pre-fetching in makeModuleResponse().
  This is already done by preloadModuleInfo() in respond().
* Don't bother storing and retreiving empty "{}" objects.
  Instead, detect whether a module's message list is empty at runtime.

ResourceLoaderModule class:
* Make logger aware.
* Log if a module's message blob was not preloaded.

cleanupRemovedModules:
* Now that blobs have a TTL, there's no need to prune old entries.

Bug: T113092
Bug: T92357
Change-Id: Id8c26f41a82597e34013f95294cdc3971a4f52ae