feat: introduce ArtplayerToolIframe for iframe control

- Removed the old ArtplayerPluginIframe implementation.
- Added ArtplayerToolIframe class with methods for iframe communication.
- Implemented postMessage and onMessage methods for message handling.
- Created a new TypeScript definition file for ArtplayerToolIframe.
- Updated documentation links to point to the new iframe tool.
- Added npm ignore file and README for the new package.
- Included compiled and uncompiled versions of the new iframe tool.
- Updated package.json with relevant metadata and exports.

packages/artplayer-tool-iframe/README.md

@@ -0,0 +1,11 @@
+# artplayer-tool-iframe
+
+Iframe tool for ArtPlayer
+
+## Demo
+
+[https://artplayer.org](https://artplayer.org/?libs=./uncompiled/artplayer-tool-iframe/index.js&example=iframe)
+
+## License
+
+MIT © Harvey Zhao