Db2 GRAPHIC and VARGRAPHIC fail row hash validation

**Describe the bug**
We should cast GRAPHIC and VARGRAPHIC values to VARCHAR before concatenating them because we get different results from `--hash`.

For example:

```
$ db2 "select col_graphic,hash(col_graphic),hash(cast(col_graphic as varchar(10))) from
pso_data_validator.dvt_db2_types;"

COL_GRAPHIC 2 3
----------- ------------------------------------ --------------------------------------
GHI x'B3163313F920AA2ED28C303C5507F161' x'81FE8A9F162D7D758AD35392D3F0BAD4'
```

**What version of DVT are you using?**
8.4.0

**What type of connections are you using for source and target?**
Db2 LUW