…s also covers add-on–related use cases; properly store updated options and store them only once).

…ating large method(s) into multiple smaller methods.

…age collect.

1. Consider {product}_data when doing garbage collection.
2. Don't garbage collect all_{module} and active_{module} since those
   have different structure and source. Add @todo to implement them
   later.
3. Properly handle missing timestamp in the garbage collector, adding
   zero risk to the existing BL.
4. Disable garbage collection by default and add it behind a flag =>
   WP_FS__ENABLE_GARBAGE_COLLECTOR.
5. Simplify some logic where possible.

…erridden during operation and how the gc timestamp is stored.

…llector