Disabling esmExternals generates a misleading warning message

[nbouvrette]

Run next info (available from version 12.0.8 and up)

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Home
Binaries:
  Node: 16.13.2
  npm: 8.3.2
  Yarn: 1.22.10
  pnpm: N/A
Relevant packages:        
  next: 12.0.8
  react: 17.0.2
  react-dom: 17.0.2  

What version of Next.js are you using?

v12.0.8

What version of Node.js are you using?

16.6

What browser are you using?

Chrome

What operating system are you using?

Windows

How are you deploying your application?

Vercel

Describe the Bug

Since Next.js 11.1.3-canary.69, ESM externals has been turned on by default using the experimental: { esmExternals: true } in this commit.

Unfortunately ESM external is still not compatible with a lot of packages and the only way to turn it off is by setting the following config:

experimental: { esmExternals: false }

The problem is that any configuration set under experimental triggers the following warning logs, which for this case seems misleading:

warn  - You have enabled experimental feature(s).
warn  - Experimental features are not covered by semver, and may cause unexpected or broken application behavior. Use them at your own risk.

This is related to #33148

Expected Behavior

I would expect that esmExternals is moved from experimental to "top-level" and stops triggering the warning.

To Reproduce

Simply set experimental: { esmExternals: false } in next.config.js