Update webpack 5 resolving (vercel#17095)

On the latest beta of webpack 5 resolving fails with the below error and according to webpack/webpack#11467 is due to the imports in this module not being fully specified. This adds the config mentioned in the thread to correct the resolving for this module. 

```sh
Failed to compile.
--
16:33:50.046 | ModuleNotFoundError: Module not found: Error: Can't resolve './assertThisInitialized' in '/vercel/f03cc85/node_modules/@babel/runtime/helpers/esm'
16:33:50.046 | > Build error occurred
16:33:50.047 | Error: > Build failed because of webpack errors
16:33:50.047 | at build (/vercel/f03cc85/node_modules/next/dist/build/index.js:15:918)
16:33:50.099 | error Command failed with exit code 1.
```

packages/next/build/webpack-config.ts

@@ -852,6 +852,18 @@ export default async function getBaseWebpackConfig(
     },
     module: {
       rules: [
+        ...(isWebpack5
+          ? [
+              // TODO: FIXME: do NOT webpack 5 support with this
+              // x-ref: https://github.com/webpack/webpack/issues/11467
+              {
+                test: /\.m?js/,
+                resolve: {
+                  fullySpecified: false,
+                },
+              } as any,
+            ]
+          : []),
         {
           test: /\.(tsx|ts|js|mjs|jsx)$/,
           include: [dir, ...babelIncludeRegexes],