Update SPFx dev guidance of SP19 & SPSE to support Node 16

Author: WesleyFive

docs/spfx/sharepoint-2019-and-subscription-edition-support.md

@@ -49,16 +49,26 @@ Microsoft recommends using the most recent version of the Yeoman generator for t
 
 1. Install [Node.js v8.17.0](https://nodejs.org/download/release/v8.17.0/).
 
-    SPFx v1.4.1 is also supported on Node.js v12 and v14 (v12.18.1 and v14.17.1 to be specific), although there's an incompatible issue [gulp 3 wasn't compatible with Node 12+](https://github.com/gulpjs/gulp/issues/2324). The workaround to resolve this issue is to specify the version of graceful-fs component as 4+. You can create npm-shrinkwrap.json in the root folder of the project and input the following content, and then run “npm install”. Also, you can use package-lock.json to resolve this issue too.
-
-    ```json
-    {
-      “dependencies”: {
-         “graceful-fs”: {
-            “version”: “4.2.2”
-          }
-       }
+   SPFx v1.4.1 is also supported on Node.js v12, v14 and v16 (v12.18.1, v14.17.1 and v16.15.0 to be specific), though there're incompatible issues ([gulp v3 is incompatible with Node v12+](https://github.com/gulpjs/gulp/issues/2324), and node-sass v4 requires Node.js v14 or below). The workaround to resolve them is to specify the version of graceful-fs component as 4+, and to replace node-sass with sass. You can manually modify `package-lock.json` or `npm-shrinkwrap.json` and then re-run `npm install`. Or you can create a new `.js` file located in the root folder of your npm project, copy the following code into that file, run `node your_new_js_file` and re-run `npm install`.
+
+    ```JavaScript
+    const fs = require('fs');
+    const lockedVersionFile = 'package-lock.json';
+    // const lockedVersionFile = 'npm-shrinkwrap.json';
+    const lockedVersionJson = JSON.parse(fs.readFileSync(lockedVersionFile));
+    if (lockedVersionJson.packages) {
+        const vinylFSJson = lockedVersionJson.packages["node_modules/vinyl-fs"];
+        if (vinylFSJson && vinylFSJson["dependencies"] && vinylFSJson["dependencies"]["graceful-fs"]) {
+            vinylFSJson["dependencies"]["graceful-fs"] = "npm:[email protected]";
+        }
+ 
+        const gulpSassJson = lockedVersionJson.packages["node_modules/gulp-sass"];
+        console.log(gulpSassJson);
+        if (gulpSassJson && gulpSassJson["dependencies"] && gulpSassJson["dependencies"]["node-sass"]) {
+            gulpSassJson["dependencies"]["node-sass"] = "npm:[email protected]";
+        }
     }
+    fs.writeFileSync(lockedVersionFile, JSON.stringify(lockedVersionJson, undefined, 2));
     ```
 
 1. Install global dependencies