[Review] fix: Fix config to make esm build esm compatible (box/box-codegen#915)

[govambam]

Recreated from box#1315 for Macroscope review.

Original PR: box#1315
Status: closed (merged)

Recreated using squash merge commit - exact merged state preserved.

Original PR: box#1315

[macroscopeapp]

Make the ESM build esm compatible by writing lib-esm/package.json with type: "module" and browser mappings for ./box/eventStream.js and ./internal/utilsNode.js

Add a postbuild script to generate lib-esm/package.json, update package.json browser mappings, switch ESM tsconfig to ES2022 with bundler resolution, and change tests to namespace imports.

📍Where to Start

Start with the build script in update-esm.mjs.

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Macroscope summarized fab73b1.