Restore `--no-mangling` CLI option for `next build` (#75921)
The `--no-mangling` CLI option for `next build` was originally
introduced in #42633. However, we lost this feature during our migration
from Terser to SWC. As part of broader improvements for debugging
dynamic accesses with Dynamic I/O enabled, I needed this functionality
back, so I restored it for Webpack and also added it to Turbopack.
fixes #67037
fixes #50208
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Co-authored-by: Benjamin Woodruff <benjamin.woodruff@vercel.com>
