to Base64 encoder function only accepts string } Uint8ARRay

## Problem

## Steps to reproduce the issue

## Expected behavior

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS:
- Visual Studio Code version:
- AWS Toolkit version:
- Amazon Q version:

Start by reproducing the Base64 encoder issue with a Uint8Array and compare it with the existing string-input behavior. The issue does not name a file, entry point, or test, so locate the encoder in the TypeScript extension and identify the relevant test coverage. Done means the encoder accepts Uint8Array input as well as strings and the behavior is covered by a test.

Written by the indexing model from the issue text.