Generalize equality of heap_lang so it works on any value.
This is more consistent with CAS, which also can be used on any value. Note that being able to (atomically) test for equality of any value and being able to CAS on any value is not realistic. See the discussion at https://gitlab.mpi-sws.org/FP/iris-coq/issues/26, and in particular JH Jourdan's observation: I think indeed for heap_lang this is just too complicated. Anyway, the role of heap_lang is not to model any actual programming language, but rather to show that we can do proofs about certain programs. The fact that you can write unrealistic programs is not a problem, IMHO. The only thing which is important is that the program that we write are realistic (i.e., faithfully represents the algorithm we want to p This commit is based on a commit by Zhen Zhang who generalized equality to work on any literal (and not just integers).