fix(replay-worker): Maintain ES5 compatibility for web worker code

[mingquan5830]

Problem

The web worker string contains ES6+ syntax that cannot be handled by tools like webpack + babel when targeting ES5 environments, which causes compatibility issues when used in projects that need to transpile to ES5.

Root Cause

I know there have been discussions about dropping ES5 support. While users who want ES5 support need to handle transpilation themselves in their projects, but web worker strings are quite special. Processing them as ES5 separately would make them compatible with more build environments.

The TypeScript configuration in packages/replay-worker/tsconfig.json was set to target: "es2018", causing the generated worker code to use modern JavaScript syntax that cannot be properly transpiled by build tools in downstream projects.

Solution

Changed the TypeScript compilation target from es2018 to es5 in the replay-worker package configuration. This ensures:

• Web worker code is generated as ES5-compatible JavaScript
• Build tools like webpack + babel can properly handle the worker code
• No breaking changes to the public API
• All existing tests continue to pass

Changes

• Modified packages/replay-worker/tsconfig.json: target: "es2018" → target: "es5"

Testing

• ✅ Existing unit tests pass
• ✅ Code quality checks (lint) pass
• ✅ Generated worker code is now ES5 compatible

[mydea]

hmm, is this change enough to actually output ES5 compatible code? 🤔 if so, then IMHO it's fine, we need to see if there is an overly big bundle size impact, but likely it's fine 🤔 cc @chargome and @billyvg thoughts?

[chargome]

Bundle size looks alright, if this does the job lgtm!

[mydea]

@chargome & @billyvg feel free to merge if you approve!