[SMTChecker] Contract invariants - simplify expressions

From https://github.com/ethereum/solidity/pull/11451

Some of the reported expressions have the following patterns which could be simplified:
```
(* (- 1) x) => -x
!(x >= y) => (x < y)
(x >= y && x <= y) => x = y
(x - y >= 0 && x - y <= 0) => x = y
```

Start with the SMTChecker context and the linked pull request 11451, then trace how contract-invariant expressions produce the reported forms. Check each listed equivalence and consider the work complete when those expressions are emitted in their simplified forms.

Written by the indexing model from the issue text.