[VL] Make ColumnarBatch::getRowBytes leak-safe

[zhztheplayer]

To make member function ColumnarBatch::getRowBytes safe in terms of memory leak.

And essential code cleanups.

[zhztheplayer]

cc @JkSelf

[JkSelf]

LGTM. Thanks.

[GlutenPerfBot]

===== Performance report for TPCH SF2000 with Velox backend, for reference only ====

query	log/native_6002_time.csv	log/native_master_06_05_2024_54aeb010d_time.csv	difference	percentage
q1	33.59	34.06	0.466	101.39%
q2	25.58	23.10	-2.483	90.29%
q3	36.47	36.59	0.116	100.32%
q4	35.01	34.70	-0.315	99.10%
q5	68.00	69.24	1.238	101.82%
q6	5.90	7.84	1.934	132.77%
q7	82.99	81.42	-1.573	98.10%
q8	86.42	87.21	0.790	100.91%
q9	118.95	119.35	0.405	100.34%
q10	43.19	45.23	2.041	104.73%
q11	20.90	22.65	1.756	108.40%
q12	25.60	25.04	-0.564	97.80%
q13	36.91	36.70	-0.213	99.42%
q14	19.27	17.35	-1.924	90.02%
q15	30.06	29.97	-0.088	99.71%
q16	14.22	15.12	0.894	106.29%
q17	100.49	104.42	3.929	103.91%
q18	146.89	144.82	-2.077	98.59%
q19	16.43	14.62	-1.811	88.98%
q20	28.49	26.48	-2.012	92.94%
q21	257.17	266.79	9.620	103.74%
q22	13.73	12.29	-1.447	89.47%
total	1246.28	1254.96	8.682	100.70%