[analyzer][solver] Fix CmpOpTable handling bug

There is an error in the implementation of the logic of reaching the `Unknonw` tristate in CmpOpTable.

```
void cmp_op_table_unknownX2(int x, int y, int z) {
  if (x >= y) {
                    // x >= y    [1, 1]
    if (x + z < y)
      return;
                    // x + z < y [0, 0]
    if (z != 0)
      return;
                    // x < y     [0, 0]
    clang_analyzer_eval(x > y);  // expected-warning{{TRUE}} expected-warning{{FALSE}}
  }
}
```
We miss the `FALSE` warning because the false branch is infeasible.

We have to exploit simplification to discover the bug. If we had `x < y`
as the second condition then the analyzer would return the parent state
on the false path and the new constraint would not be part of the State.
But adding `z` to the condition makes both paths feasible.

The root cause of the bug is that we reach the `Unknown` tristate
twice, but in both occasions we reach the same `Op` that is `>=` in the
test case. So, we reached `>=` twice, but we never reached `!=`, thus
querying the `Unknonw2x` column with `getCmpOpStateForUnknownX2` is
wrong.

The solution is to ensure that we reached both **different** `Op`s once.

Differential Revision: https://reviews.llvm.org/D110910