Strip `assetPrefix` when resolving external source maps of client chunks (#72258)
When using Turbopack, and importing a server action into a client
component, the source map for the client chunk will be requested if
devtools are open. The filename for this source map request might be
`/_next/static/chunks/[project]__800ed2._.js`, for example. This
scenario was already handled by the dev middleware.
However, it didn't consider that there might also be an `assetPrefix`
defined in the `next.config.js`. In this case, the filename would be
`/some-asset-prefix/_next/static/chunks/[project]__800ed2._.js`. When
resolving the external source map for this file, we need to strip the
asset prefix.
Again, this can only be tested manually.