Turbopack: fix `@opentelemetry/api` resolve fallback (#81541)
Previously, it tried `[project]/node_modules/@opentelemetry/api` and then fell back to `node_modules/next/dist/compiled/@opentelemetry/api`.
But that doesn't work if the dependency is installed in a monorepo subpackage and should have been resolved from `packages/my-app/node_modules/@opentelemetry/api`.
We already have `fallback_import_map` which is exactly what's needed here.
Closes PACK-5054
