Use brackets to access array elements

Summary:
Fixes the following issue:
[28-Nov-2024 20:07:37 UTC] PHP Fatal error:
Array and string offset access syntax with curly braces is no longer supported
in .../sourcetemplatesgenerator/helpers/Encoding.php

Test Plan: Tested on tools51.nasqueron.org

Reviewers: MoustaphaAs

Reviewed By: MoustaphaAs

Differential Revision: https://devcentral.nasqueron.org/D3607