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ARROW-12866: [C++][Gandiva] Implement STRPOS function on Gandiva

Search for a string within another string.
Same as "LOCATE(substr, str)", except for the reverse order of the arguments STRPOS(str, substr).

Closes #10396 from jpedroantunes/feature/add-str-pos and squashes the following commits:

a407ac1aa <João Pedro> Fix linter errors
0f3a8ec84 <João Pedro> Add strpos function definition and registry

Authored-by: João Pedro <joaop@simbioseventures.com>
Signed-off-by: Praveen <praveen@dremio.com>