[next] Add i18n support handling (#5298)

* Add initial locale output mapping

* Add additional probes

* Add locale specific 404 handling

* Add locale specific 404s, locale redirects, and more tests

* Update wildcard value

* Fix wildcard handling and update route type

* Update addLocale util

* Apply suggestions from code review

Co-authored-by: Steven <steven@ceriously.com>

* Remove redundant console.error

Co-authored-by: Steven <steven@ceriously.com>
Co-authored-by: Leo Lamprecht <leo@zeit.co>

packages/now-next/package.json

@@ -29,7 +29,7 @@
     "@vercel/nft": "0.9.2",
     "async-sema": "3.0.1",
     "buffer-crc32": "0.2.13",
-    "escape-string-regexp": "3.0.0",
+    "escape-string-regexp": "2.0.0",
     "execa": "2.0.4",
     "find-up": "4.1.0",
     "fs-extra": "7.0.0",