…re in the sysimage

When triggers of extension are in the sysimage it is easy to end up with cycles in package loading.
Say we have a package A with exts BExt and CExt and say that B and C is in the sysimage.

- Upon loading A, we will immidiately start to precompile BExt (because the trigger B is "loaded" by virtue of being in the sysimage).
- BExt will load A which will cause CExt to start precompiling (again because C is in the sysimage).
- CExt will load A which will now cause BExt to start loading and we get a cycle.

This is fixed in this PR by instead of looking at what modules are loaded, we look at what modules are actually `require`d
and only use that to drive the loading of extensions.

…n the sysimage