Chore(repo): Introduce Yarn plugin for overriding state

  * this should solve the problem with non-existing node modules
    state file
  * @see: heroku/heroku-buildpack-nodejs#907

.yarn/plugins/plugin-override-state.js

@@ -0,0 +1,31 @@
+const ALLOWED_SCRIPTS=["build"];
+
+const NODE_MODULES="node_modules";
+const STATE_FILE=".yarn-state.yml";
+
+module.exports = {
+  name: `plugin-override-state`,
+  factory: require => ({
+    hooks: {
+      async setupScriptEnvironment(project, scriptEnv) {
+        if (scriptEnv != null && ALLOWED_SCRIPTS.find(script => script == scriptEnv.npm_lifecycle_event) != null) {
+          if (project.configuration.get(`nodeLinker`) === `node-modules`) {
+            const stateFile = [project.cwd, NODE_MODULES, STATE_FILE].join("/");
+            const fs = require("fs");
+
+            if (!fs.existsSync(stateFile)) {
+              console.log("Detected command allowed in stateless environment and state file is missing.");
+              console.log("Generating empty state file...");
+
+              fs.mkdirSync(require('path').dirname(stateFile), { recursive: true });
+              fs.appendFileSync(stateFile, "# Autogenerated\n", {"flag":"w+"});
+              fs.appendFileSync(stateFile, "__metadata:\n");
+              fs.appendFileSync(stateFile, "  version: 1\n");
+              fs.appendFileSync(stateFile, "  nmMode: classic\n");
+            }
+          }
+        }
+      }
+    },
+  })
+};

.yarnrc.yml

@@ -7,3 +7,4 @@ nodeLinker: node-modules
 plugins:
   - path: .yarn/plugins/@yarnpkg/plugin-engines.cjs
     spec: 'https://raw.githubusercontent.com/devoto13/yarn-plugin-engines/main/bundles/%40yarnpkg/plugin-engines.js'
+  - .yarn/plugins/plugin-override-state.js