Snowflake: support position with normal function call syntax

[jmhain]

On Snowflake, the special IN syntax is optional: https://docs.snowflake.com/en/sql-reference/functions/position. This PR updates the parser to accept this.

[coveralls]

Pull Request Test Coverage Report for Build 10133397097

Details

• 27 of 28 (96.43%) changed or added relevant lines in 3 files are covered.
• 13 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.03%) to 89.222%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tests/sqlparser_common.rs	12	13	92.31%

Files with Coverage Reduction	New Missed Lines	%
src/ast/query.rs	1	85.93%
src/parser/mod.rs	1	93.32%
tests/sqlparser_common.rs	4	89.6%
src/lib.rs	7	12.64%

Totals
Change from base Build 10063291795:	-0.03%
Covered Lines:	27203
Relevant Lines:	30489

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💛 - Coveralls

[alamb]

I think the comments from @iffyio and @git-hulk are good. Once those get done I think this PR is good to go.

Thanks everyone

[jmhain]

@iffyio @alamb Addressed the comments. Sorry for the delay in getting back to this!

[iffyio]

LGTM! cc @alamb

[alamb]

Thank you @jmhain @iffyio and @git-hulk