[VL] Fix StringToMap test failure

[PHILO-HE]

What changes were proposed in this pull request?

Gluten + Velox backend only supports the default SQLConf.MapKeyDedupPolicy.EXCEPTION policy. This PR adds the check to make it fall back on unsupported config.

How was this patch tested?

Existing Spark UT covers it.

[github-actions]

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Could you open an issue for this pull request on Github Issues?

https://github.com/oap-project/gluten/issues

Then could you also rename commit message and pull request title in the following format?

[GLUTEN-${ISSUES_ID}][COMPONENT]feat/fix: ${detailed message}

See also:

• Other pull requests

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[GlutenPerfBot]

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

query	log/native_3995_time.csv	log/native_master_12_10_2023_e9ea4e3e4_time.csv	difference	percentage
q1	33.56	34.68	1.121	103.34%
q2	25.87	27.19	1.326	105.12%
q3	37.93	37.58	-0.348	99.08%
q4	39.54	37.98	-1.561	96.05%
q5	70.89	70.50	-0.393	99.45%
q6	7.10	6.93	-0.176	97.52%
q7	85.26	84.23	-1.032	98.79%
q8	86.95	85.45	-1.491	98.28%
q9	127.36	126.22	-1.142	99.10%
q10	43.57	43.28	-0.295	99.32%
q11	20.65	19.94	-0.713	96.55%
q12	28.43	27.48	-0.957	96.63%
q13	47.03	47.58	0.547	101.16%
q14	15.26	16.51	1.245	108.15%
q15	28.52	27.43	-1.088	96.19%
q16	16.01	15.68	-0.328	97.95%
q17	103.72	104.55	0.830	100.80%
q18	150.13	149.27	-0.861	99.43%
q19	12.89	13.60	0.706	105.47%
q20	27.48	27.18	-0.297	98.92%
q21	225.13	225.87	0.738	100.33%
q22	13.96	13.10	-0.855	93.87%
total	1247.24	1242.22	-5.026	99.60%