feat: move compat database to separate package

The packageExtensions compat database is useful for pnpm as well.
By moving it to a separate package, we can use it in pnpm and
recommend the pnpm users to extend the database as well.

Author: zkochan

.pnp.cjs

@@ -0,0 +1,5 @@
+releases:
+  "@yarnpkg/extensions": minor
+
+declined:
+  - "@yarnpkg/plugin-compat"

.yarn/versions/1633b796.yml

@@ -0,0 +1,9 @@
+# `@yarnpkg/extensions`
+
+This package contains package extensions that fix known issues in the ecosystem
+
+## Install
+
+```
+yarn add @yarnpkg/extensions
+```

packages/extensions/README.md

@@ -0,0 +1,6 @@
+// plugin-compat is tested separately, as it relies on external resources
+// and it takes a long time for them to be fetched
+
+module.exports = Object.assign({}, require(`@yarnpkg/monorepo/jest.config.js`), {
+  modulePathIgnorePatterns: [],
+});

packages/extensions/jest.config.js

@@ -0,0 +1,34 @@
+{
+  "name": "@yarnpkg/extensions",
+  "version": "0.0.0",
+  "license": "BSD-2-Clause",
+  "main": "./sources/index.ts",
+  "peerDependencies": {
+    "@yarnpkg/core": "workspace:^"
+  },
+  "devDependencies": {
+    "@yarnpkg/core": "workspace:^",
+    "@yarnpkg/monorepo": "workspace:^"
+  },
+  "repository": {
+    "type": "git",
+    "url": "ssh://[email protected]/yarnpkg/berry.git",
+    "directory": "packages/extensions"
+  },
+  "scripts": {
+    "postpack": "rm -rf lib",
+    "prepack": "run build:compile \"$(pwd)\"",
+    "test:extensions": "run test:unit --config \"$(pwd)/jest.config.js\"",
+    "debug:patch": "node -r @yarnpkg/monorepo/scripts/setup-ts-execution extra/debugPatch \"$INIT_CWD\""
+  },
+  "publishConfig": {
+    "main": "./lib/index.js",
+    "typings": "./lib/index.d.ts"
+  },
+  "files": [
+    "/lib/**/*"
+  ],
+  "engines": {
+    "node": ">=14.15.0"
+  }
+}