Prior to this commit, attempting to use a custom java plugin installed from rubygems would
fail as the `files` field used to find jar files in the gem is not populated for such gems
This commit uses the `full_require_path` to find the jar file for a native jar plugin,
which should work regardless of where the gem was installed from, locally or via rubygems
Additionally, this commit will only attempt to locate the jar file inside the gem when it
is required (only when the experimental separate plugin class loader is used)
This commit builds on the work done in #13888
Relates: #13888, #11305
Co-authored-by: twosom <two_somang@icloud.com>
Co-authored-by: Ry Biesemeyer <yaauie@users.noreply.github.com>
