[GR-57591] Implement Uint8Array to/from base64 and hex

[fniephaus]

TL;DR

We plan to implement Uint8Array to/from base64 and hex in GraalJS.

Details

Base64 is a common way to represent arbitrary binary data as ASCII. JavaScript has Uint8Arrays to work with binary data, but no built-in mechanism to encode that data as base64, nor to take base64'd data and produce a corresponding Uint8Arrays. This is a proposal to fix that. It also adds methods for converting between hex strings and Uint8Arrays.