[native][utils-module] Implement base64 encode

Summary:
Part of ENG-3408.This one implements base64 encode, which replaces the slow JS implementation.

This implementation is inspired by this article but it is somehow modified (original article impl requires C++20).

Depends on D7485

Test Plan: Called this from JS for various cases and compared it with online converter. Results are equal for each padding value (0, 1, 2).

Reviewers: marcin, kamil, inka

Reviewed By: kamil

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7486