Update Browser Build for Deno 2

[aunyks]

TL;DR

• Uses esbuild-deno-loader as a replacement for deno bundle (now deprecated)
• Updates vfs.js, which supports the browser build, to be in line with the local build
• Uses deno.json to handle import maps (standard in Deno 2) for the browser build
• Updates README.md in line with the above changes

Notes for Reviewers

• The formatting changes in vfs.js arise from running deno fmt against the file

[dyedgreen]

Hey, sorry for taking a while to get back to this!

This change looks great, outside of a few files that are flagged by the formatting in CI 👀

(Some of those have not changed in a while so they might have changed the formatting in Deno?)