[sledge] Strengthen Z3 encoding with seg validity constraints
[sledge] Strengthen Z3 encoding with seg validity constraints

Summary:
Add the validity constraints on individual segments. In particular:
```
k-[b;m)->⟨n,α⟩ |-
(m >= 0) * (n >= 0) * (k >= b) * (k+n <= b+m) * (n = 0 <=> m = 0)
```

Also, as a partial work-around for the lack of sorts in sledge, assert
that all free variables in address and size terms are integral.

Reviewed By: bennostein

Differential Revision: D39136452

fbshipit-source-id: 6065d726f6a8d7f83b3f4cf783946b57f6b03618

facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer