make sure "webpack" exists in the repo for typings (#30371)

fixes "yarn types" needed before "yarn dev"
use incremental typescript for next package

.gitignore

@@ -39,3 +39,6 @@ test-timings.json
 # Vercel
 .vercel
 .now
+
+# Cache
+*.tsbuildinfo

package.json

@@ -156,6 +156,7 @@
     "typescript": "4.4.3",
     "wait-port": "0.2.2",
     "web-streams-polyfill": "2.1.1",
+    "webpack": "link:./node_modules/webpack5",
     "webpack-bundle-analyzer": "4.3.0",
     "worker-loader": "3.0.7"
   },

packages/next/tsconfig.json

@@ -5,7 +5,8 @@
     "target": "ES2017",
     "esModuleInterop": true,
     "moduleResolution": "node",
-    "jsx": "react"
+    "jsx": "react",
+    "incremental": true
   },
   "exclude": ["dist", "./*.d.ts"]
 }

yarn.lock

@@ -19883,6 +19883,10 @@ webpack-sources@^3.2.0:
     watchpack "^2.2.0"
     webpack-sources "^3.2.0"
 
+"webpack@link:./node_modules/webpack5":
+  version "0.0.0"
+  uid ""
+
 websocket-driver@>=0.5.1:
   version "0.7.3"
   resolved "https://registry.yarnpkg.com/websocket-driver/-/websocket-driver-0.7.3.tgz#a2d4e0d4f4f116f1e6297eba58b05d430100e9f9"