Revert "[Truffle] Remove now useless (and incorrect!) AddNode specialization."

This reverts commit 27712b71b4dd926ccce96e81746a84e559611057.
[Truffle] Fix Fixnum#+(int,long) specializations.
Revert "[Truffle] Introduce ImplicitCast from int to long."

This reverts commit 032326dbe04ae91ac79bf3b9ef2340e8df74b67e.