Migrate to yarn v4

Use yarn PnP which forces us to install some more explicit dependencies.

Change-Id: Ib35c5c71a37081c98778937bde5a23bf997dd54c

.vscode/extensions.json

@@ -0,0 +1,7 @@
+{
+  "recommendations": [
+    "arcanis.vscode-zipfs",
+    "dbaeumer.vscode-eslint",
+    "esbenp.prettier-vscode"
+  ]
+}