templates(express): use watcher.on("add").on("change")

[xHomu]

Also add in comments on what to change for CJS

Does not close #6919 but the debugger might help with bug tracking.

• Docs

This actually get the express template in line with existing v2 dev doc changes.

Testing Strategy:

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[ngbrown]

chokidar isn't a production dependency, so it would be better to use (await import("chokidar")), remove the chokidar import at the top of the file, make createDevRequestHandler() async, and await on it at the app.all() handler.

[xHomu]

Updated the patch to use await import, not sure if it's the best way to write this?

[ngbrown]

In my code, I imported directly in the createDevRequestHandler() function, but this way is probably the cleanest if swapping in CJS is important.

[MichaelDeBoey]

@pcattori @xHomu Is this still relevant now that #7303 is merged?

[xHomu]

Probably not. Should close this and rewrite express server.js with updated syntax.

[ngbrown]

These changes also updated the template to address the race condition described in #6831/#6919. The changes in #7303 didn't address that.