Upgrade edge-runtime + make EdgeRuntime value overridable with an env…

… var on compilation (#38331)

This PR introduces an environment variable that allows to modify the `EdgeRuntime` value on compilation time.
This is done to allow cloud providers like Vercel to have a different value, and enable user code and 3rd party libraries to have different code paths depending on the Edge Functions provider.

## Related

- Related to #30739

## Bug

- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

package.json

@@ -55,7 +55,7 @@
     "@babel/plugin-proposal-object-rest-spread": "7.14.7",
     "@babel/preset-flow": "7.14.5",
     "@babel/preset-react": "7.14.5",
-    "@edge-runtime/jest-environment": "1.1.0-beta.10",
+    "@edge-runtime/jest-environment": "1.1.0-beta.11",
     "@fullhuman/postcss-purgecss": "1.3.0",
     "@mdx-js/loader": "0.18.0",
     "@next/bundle-analyzer": "workspace:*",

packages/next/build/webpack-config.ts

@@ -1497,7 +1497,14 @@ export default async function getBaseWebpackConfig(
         ...(compilerType !== 'edge-server'
           ? {}
           : {
-              EdgeRuntime: JSON.stringify('edge-runtime'),
+              EdgeRuntime: JSON.stringify(
+                /**
+                 * Cloud providers can set this environment variable to allow users
+                 * and library authors to have different implementations based on
+                 * the runtime they are running with, if it's not using `edge-runtime`
+                 */
+                process.env.NEXT_EDGE_RUNTIME_PROVIDER || 'edge-runtime'
+              ),
             }),
         // TODO: enforce `NODE_ENV` on `process.env`, and add a test:
         'process.env.NODE_ENV': JSON.stringify(