Prepare index.js as the new entry point

This somewhat restores the module's public API to that before 91e5e73, by adding back the propertyDescriptors export. However, it is now a Map instead of an object, so it remains a breaking change.

Author: asamuzaK

lib/index.js

@@ -0,0 +1,9 @@
+"use strict";
+
+const { CSSStyleDeclaration } = require("./CSSStyleDeclaration");
+const propertyDefinitions = require("./generated/propertyDefinitions");
+
+module.exports = {
+  CSSStyleDeclaration,
+  propertyDefinitions
+};

package.json

@@ -14,7 +14,7 @@
   "files": [
     "lib/"
   ],
-  "main": "./lib/CSSStyleDeclaration.js",
+  "main": "./lib/index.js",
   "dependencies": {
     "@asamuzakjp/css-color": "^4.1.1",
     "@csstools/css-syntax-patches-for-csstree": "^1.0.24",