fix: allow snowflake to accept values without parens

[HiranmayaGundu]

Snowflake and Databricks both allow:

"SELECT * FROM VALUES (1, 2), (2,3) AS tbl (id, val)";

this adds support for that

[coveralls]

Pull Request Test Coverage Report for Build 8943938289

Details

• 44 of 48 (91.67%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 89.187%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser/mod.rs	16	17	94.12%
tests/sqlparser_common.rs	28	31	90.32%

Totals
Change from base Build 8943500950:	0.02%
Covered Lines:	24225
Relevant Lines:	27162

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💛 - Coveralls

[alamb]

LGTM -- thank you @HiranmayaGundu