Currently, during application startup we:
  * copy the FLX file to a Mojo pipe
  * write the Mojo pipe contents back to a temporary file on disk
  * unzip the FLX contents into cache storage
This contributes to startup latency and requires that we later clean up the
cache.

With this change, the assets will be extracted from the FLX archive
on demand with no writes to storage. Runtime cost should be minimal
given that most assets (except for the snapshot) are not compressed
in the archive.