fix(webpack): add comment to explain useLegacyNxPlugin and how to remove it (#26696)

This PR adds a comment when `useLegacyNxPlugin` is used so users know
what it is, and how they can remove it.

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## Current Behavior
<!-- This is the behavior we have today -->

## Expected Behavior
<!-- This is the behavior we should expect with the changes in this PR
-->

## Related Issue(s)
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merged. -->

Fixes #

e2e/webpack/src/__snapshots__/webpack.legacy.test.ts.snap

@@ -20,6 +20,10 @@ module.exports = async () => ({
       // See: https://react-svgr.com/
       // svgr: false
     }),
+    // NOTE: useLegacyNxPlugin ensures that the non-standard Webpack configuration file previously used still works.
+    // To remove its usage, move options such as "plugins" into this file as standard Webpack configuration options.
+    // To enhance configurations after Nx plugins have applied, you can add a new plugin with the \\\`apply\\\` method.
+    // e.g. \\\`{ apply: (compiler) => { /* modify compiler.options */ }\\\`
     // eslint-disable-next-line react-hooks/rules-of-hooks
     await useLegacyNxPlugin(require('./webpack.config.old'), options),
   ],

packages/webpack/src/generators/convert-config-to-webpack-plugin/convert-config-to-webpack-plugin.spec.ts

@@ -134,6 +134,10 @@ describe('convertConfigToWebpackPluginGenerator', () => {
             // See: https://react-svgr.com/
             // svgr: false
           }),
+          // NOTE: useLegacyNxPlugin ensures that the non-standard Webpack configuration file previously used still works.
+          // To remove its usage, move options such as "plugins" into this file as standard Webpack configuration options.
+          // To enhance configurations after Nx plugins have applied, you can add a new plugin with the \\\`apply\\\` method.
+          // e.g. \\\`{ apply: (compiler) => { /* modify compiler.options */ }\\\`
           // eslint-disable-next-line react-hooks/rules-of-hooks
           await useLegacyNxPlugin(require('./webpack.config.old'), options),
         ],
@@ -419,6 +423,10 @@ describe('convertConfigToWebpackPluginGenerator', () => {
             // See: https://react-svgr.com/
             // svgr: false
           }),
+          // NOTE: useLegacyNxPlugin ensures that the non-standard Webpack configuration file previously used still works.
+          // To remove its usage, move options such as "plugins" into this file as standard Webpack configuration options.
+          // To enhance configurations after Nx plugins have applied, you can add a new plugin with the \\\`apply\\\` method.
+          // e.g. \\\`{ apply: (compiler) => { /* modify compiler.options */ }\\\`
           // eslint-disable-next-line react-hooks/rules-of-hooks
           await useLegacyNxPlugin(require('./webpack.config.old'), options),
         ],

packages/webpack/src/generators/convert-config-to-webpack-plugin/convert-config-to-webpack-plugin.ts

@@ -111,6 +111,10 @@ export async function convertConfigToWebpackPluginGenerator(
                   // svgr: false
                   })`
                 },
+                // NOTE: useLegacyNxPlugin ensures that the non-standard Webpack configuration file previously used still works.
+                // To remove its usage, move options such as "plugins" into this file as standard Webpack configuration options.
+                // To enhance configurations after Nx plugins have applied, you can add a new plugin with the \`apply\` method.
+                // e.g. \`{ apply: (compiler) => { /* modify compiler.options */ }\`
                 // eslint-disable-next-line react-hooks/rules-of-hooks
                 await useLegacyNxPlugin(require('./webpack.config.old'), options),
               ],