Use hash value checks optimizations consistently

There are couple of optimizations of `__hash_table::find` which are applicable
to other places like `__hash_table::__node_insert_unique_prepare` and
`__hash_table::__emplace_unique_key_args`.

```
for (__nd = __nd->__next_; __nd != nullptr &&
    (__nd->__hash() == __hash
    // ^^^^^^^^^^^^^^^^^^^^^^
    //         (1)
      || std::__constrain_hash(__nd->__hash(), __bc) == __chash);
                                               __nd = __nd->__next_)
{
    if ((__nd->__hash() == __hash)
    // ^^^^^^^^^^^^^^^^^^^^^^^^^^
    //           (2)
        && key_eq()(__nd->__upcast()->__value_, __k))
        return iterator(__nd, this);
}
```

(1): We can avoid expensive modulo operations from `std::__constrain_hash` if
hashes matched. This one is from commit 6a411472.
(2): We can avoid `key_eq` calls if hashes didn't match. Commit:
318d35a7.

Both of them are applicable for insert and emplace methods.

Results of unordered_set_operations benchmark:
...