fix(gatsby-link): Correctly export default for CJS (#36312)

Co-authored-by: pieh <misiek.piechowiak@gmail.com>
Co-authored-by: LekoArts <lekoarts@gmail.com>

Author: 3 people

packages/gatsby-link/package.json

@@ -6,7 +6,6 @@
   "bugs": {
     "url": "https://github.com/gatsbyjs/gatsby/issues"
   },
-  "source": "src/index.js",
   "main": "dist/index.js",
   "module": "dist/index.modern.mjs",
   "types": "index.d.ts",
@@ -16,8 +15,12 @@
   ],
   "sideEffects": false,
   "scripts": {
-    "build": "microbundle -f cjs,modern --jsx React.createElement --generateTypes false",
-    "watch": "npm run build watch --no-compress",
+    "build": "npm-run-all --npm-path npm -s build:cjs build:esm",
+    "build:cjs": "microbundle -f cjs --jsx React.createElement --generateTypes false  -i src/index-cjs.js -o dist/index.js",
+    "build:esm": "microbundle -f modern --jsx React.createElement --generateTypes false -o dist/index.mjs",
+    "watch": "npm-run-all --npm-path npm -p watch:cjs watch:esm",
+    "watch:cjs": "npm run build:cjs watch --no-compress",
+    "watch:esm": "npm run build:esm watch --no-compress",
     "prepare": "cross-env NODE_ENV=production npm run clean && npm run build",
     "clean": "del-cli dist/*"
   },
@@ -30,7 +33,8 @@
     "@testing-library/react": "^11.2.7",
     "cross-env": "^7.0.3",
     "del-cli": "^5.0.0",
-    "microbundle": "^0.15.0"
+    "microbundle": "^0.15.0",
+    "npm-run-all": "^4.1.5"
   },
   "peerDependencies": {
     "@gatsbyjs/reach-router": "^1.3.5",
@@ -50,4 +54,4 @@
   "engines": {
     "node": ">=14.15.0"
   }
-}
+}

packages/gatsby-link/src/index-cjs.js

@@ -0,0 +1,10 @@
+import * as Link from "./index.js"
+
+module.exports = Link.default
+
+Object.getOwnPropertyNames(Link).forEach(key => {
+  Object.defineProperty(module.exports, key, {
+    value: Link[key],
+    enumerable: true,
+  })
+})