This was leading to far too many hard-to-debug bugs, and was a significant
source of confusion in various parts of the codebase. Allowing one plugin to
access a GsApp managed by another plugin was sometimes useful, but came at a
huge cognitive cost when working out when the unique-id was "good enough" to
add a GsApp to the shared pool.

Using the _refine_wildcard() vfunc like originally intended allows us an easy
way to 'get' a GsApp just from an optionally-globbed unique-id string.