Move resolveExtensions config up to experimental

[LichuAcu]

What?

Moves resolveExtensions up from experimental.turbo to experimental in next.config.js. Makes Webpack configuration also read from that field.

Closes PACK-2578

[ijjk]

Allow CI Workflow Run

• [ ] approve CI run for commit: f0b70cab95244ad0b2722059c2835853f2511385

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[wbinnssmith]

this is a breaking change — anyone with this field set in experimental.turbo will have it stop working. but imo this is okay:

• the field is in experimental, which is subject to change
• canary is going to be next.js 15, where we’re allowing breaking changes

@timneutkens is any documentation/communication about this necessary?

[LichuAcu]

• #69108
• #67399 👈
• canary

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[ijjk]

Tests Passed