[Gandiva][C++] Add TRUNC function

[asfimport]

Returns date truncated to the unit specified by the format. Supported formats: MONTH/MON/MM, YEAR/YYYY/YY. Example: trunc('2015-03-17', 'MM') = 2015-03-01.

Reporter: Johnnathan Rodrigo Pego de Almeida / @Johnnathanalmeida

PRs and other links:

• GitHub Pull Request #12405

_{Note: This issue was originally created as ARROW-15663. Please see the migration documentation for further details.}

[asfimport]

ZMZ91 / @ZMZ91:
will this handle timezone?

[github-actions]

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