Prevent unpredictable dependency hosting by explicitly resolve module…

… path on webpack.ProvidePlugin (#20971)

ProvidePlugin replaces certain identifiers with another modules. As a result, 'buffer' and 'process' modules are added as implicit dependencies to all Next.js plugins. This can be problematic. With "Plug'n'Play" strategy, it don't work at all since they fail-fast with implicit dependencies. With "node_modules" strategy, it might seem OK but actually it can be result into unpredictable behavior since in uses dependency [hoisting](https://yarnpkg.com/advanced/lexicon#hoisting).

For example, currently users cannot use next-auth plugin with Plug'n'Play strategy:

![image](https://user-images.githubusercontent.com/4435445/103481517-d5547700-4e1e-11eb-9f23-bc2c9939418e.png)

This patch let Next.js properly handles such cases with `require.resolve`.

Closes #20955

###### References:
- nextauthjs/next-auth#1034

packages/next/build/webpack-config.ts

@@ -911,14 +911,13 @@ export default async function getBaseWebpackConfig(
     },
     plugins: [
       hasReactRefresh && new ReactRefreshWebpackPlugin(),
-      // Makes sure `Buffer` is polyfilled in client-side bundles (same behavior as webpack 4)
+      // Makes sure `Buffer` and `process` are polyfilled in client-side bundles (same behavior as webpack 4)
       isWebpack5 &&
         !isServer &&
-        new webpack.ProvidePlugin({ Buffer: ['buffer', 'Buffer'] }),
-      // Makes sure `process` is polyfilled in client-side bundles (same behavior as webpack 4)
-      isWebpack5 &&
-        !isServer &&
-        new webpack.ProvidePlugin({ process: ['process'] }),
+        new webpack.ProvidePlugin({
+          Buffer: [require.resolve('buffer'), 'Buffer'],
+          process: [require.resolve('process')],
+        }),
       // This plugin makes sure `output.filename` is used for entry chunks
       !isWebpack5 && new ChunkNamesPlugin(),
       new webpack.DefinePlugin({