Fallback to stored funcs in LazyLoader

This corrects issues wherein some functions are not available inside
the context of certain modules.

This is a pretty simple fix, so by all means please let me know if
it's too naieve. I'm simply falling back to a stored functions if
we try to LazyLoad a function that's not a part of the loader owned
by LL in question. (i.e., trying to load an exec module into a
returner.)

Closes #12641

This needs careful review from @jacksontj and @thatch45