feat: add Document Picture-in-Picture plugin for ArtPlayer

- Implemented the core functionality of the Document Picture-in-Picture plugin.
- Created main plugin file `artplayer-plugin-document-pip.js` with support for opening and closing the PIP window.
- Added legacy support in `artplayer-plugin-document-pip.legacy.js`.
- Defined plugin options in `package.json` and included necessary metadata.
- Developed the main logic in `src/index.js`, including style copying and event handling.
- Created TypeScript definitions in `types/artplayer-plugin-document-pip.d.ts` for better type safety.

packages/artplayer-plugin-document-pip/package.json

@@ -0,0 +1,24 @@
+{
+  "name": "artplayer-plugin-document-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-document-pip.js",
+  "types": "types/artplayer-plugin-document-pip.d.ts",
+  "legacy": "dist/artplayer-plugin-document-pip.legacy.js",
+  "browserslist": "last 1 Chrome version"
+}