feat: add Picture-in-Picture plugin for ArtPlayer

- Introduced `artplayer-plugin-pip` to enable Picture-in-Picture functionality.
- Updated `artplayer.d.ts` to export new types related to the plugin.
- Added example usage of the plugin in `pip.js`.
- Created TypeScript definitions for the plugin in `artplayer-plugin-pip.d.ts`.
- Implemented the plugin logic in `index.js` with necessary styles and event handling.
- Updated documentation to include the new plugin and its usage.
- Added README and package.json for the new plugin.

packages/artplayer-plugin-pip/package.json

@@ -0,0 +1,24 @@
+{
+  "name": "artplayer-plugin-pip",
+  "version": "1.0.0",
+  "description": "pip plugin for ArtPlayer",
+  "author": "Harvey Zack <laozhaochaguan@gmail.com>",
+  "license": "MIT",
+  "homepage": "https://artplayer.org",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/zhw2590582/ArtPlayer.git"
+  },
+  "bugs": {
+    "url": "https://github.com/zhw2590582/ArtPlayer/issues"
+  },
+  "keywords": [
+    "html5",
+    "video",
+    "player"
+  ],
+  "main": "dist/artplayer-plugin-pip.js",
+  "types": "types/artplayer-plugin-pip.d.ts",
+  "legacy": "dist/artplayer-plugin-pip.legacy.js",
+  "browserslist": "last 1 Chrome version"
+}