using hex string as bindvar for decimal type column in prepared statement causes panic

Repro enginetest:
```
{
Name: "simple decimal type insert",
SetUpScript: []string{
"CREATE TABLE test(id int primary key auto_increment, decimal_col DECIMAL(9,2))",
},
Assertions: []queries.ScriptTestAssertion{
{
Query: "INSERT INTO test(decimal_col) VALUES (?)",
Bindings: map[string]sql.Expression{
"v1": expression.NewLiteral([]byte("X'10'"), sql.MustCreateString(sqltypes.VarBinary, 4, sql.Collation_binary)),
},
Expected: []sql.Row{
{sql.OkResult{RowsAffected: 1, InsertID: 1}},
},
},
},
},
```

Using Literal of `X'10'` with `VarBinary` type is because most types are handled as `VarBinary` in https://github.com/dolthub/vitess/blob/main/go/mysql/query.go#L842 when we get parse the bindvars, so the hex string is handled the same way as any other string values.