provide ILIKE support

[maxcountryman]

This introduces support for ILIKE and NOT ILIKE. ILIKE is the
case-insensitive variant of LIKE. Systems such as Postgres, Redshift,
and Snowflake provide this variant.[1][2][3]

[1] https://www.postgresql.org/docs/7.3/functions-matching.html
[2] https://docs.aws.amazon.com/redshift/latest/dg/r_patternmatching_condition_like.html
[3] https://docs.snowflake.com/en/sql-reference/functions/ilike.html

[coveralls]

Pull Request Test Coverage Report for Build 676366782

• 33 of 36 (91.67%) changed or added relevant lines in 4 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.008%) to 90.054%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/mod.rs	0	1	0.0%
src/parser.rs	7	9	77.78%

Files with Coverage Reduction	New Missed Lines	%
src/parser.rs	1	86.11%

Totals
Change from base Build 674150113:	0.008%
Covered Lines:	5460
Relevant Lines:	6063

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💛 - Coveralls

[maxcountryman]

This lint issue seems to also happen on main.

[Dandandan]

looks good! could you merge/rebase to get in the clippy lint fixes?