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GH-40727: [C++][Gandiva] 'ilike' function does not work (#40728)

### Rationale for this change

Bug fix for GH-40727

### What changes are included in this PR?

Register the 'ilike' function.
Added unit test.

### Are these changes tested?

Yes, unit test.

### Are there any user-facing changes?

No.

* GitHub Issue: #40727

Authored-by: Logan Riggs <logan.riggs@dremio.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>