staticdata: Insert backedges recursively (#57212)
In the new edges scheme, when we perform constant propagation, we create
a dummy CodeInstance that is not inserted into the specializations
cache, but instead simply serves as a container for all edges that were
encountered during the constant propagation. These CodeInstances are not
part of either the internal or external edges list collected during
pkgimage generation. As such, while we were verifying edges recursively
and would thus catch an invalidation prior to package image reload, we
were failing to also insert backedges for these CodeInstance. We were
thus failing to invalidate such methods if the method was redefined
after re-load of the package image. Fix that by moving the storing of
the backedges to the end of the validation code, so that it too happens
recursively.
