Migrate to yarn v4

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

Change-Id: Ib35c5c71a37081c98778937bde5a23bf997dd54c

.yarn/sdks/prettier/index.cjs

@@ -0,0 +1,20 @@
+#!/usr/bin/env node
+
+const {existsSync} = require(`fs`);
+const {createRequire} = require(`module`);
+const {resolve} = require(`path`);
+
+const relPnpApiPath = "../../../.pnp.cjs";
+
+const absPnpApiPath = resolve(__dirname, relPnpApiPath);
+const absRequire = createRequire(absPnpApiPath);
+
+if (existsSync(absPnpApiPath)) {
+  if (!process.versions.pnp) {
+    // Setup the environment to be able to require prettier
+    require(absPnpApiPath).setup();
+  }
+}
+
+// Defer to the real prettier your application uses
+module.exports = absRequire(`prettier`);