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.

docs/assets/js/common.js

@@ -63,7 +63,6 @@
       './assets/ts/artplayer-plugin-dash-control.d.ts',
       './assets/ts/artplayer-plugin-document-pip.d.ts',
       './assets/ts/artplayer-plugin-hls-control.d.ts',
-      './assets/ts/artplayer-plugin-iframe.d.ts',
       './assets/ts/artplayer-plugin-jassub.d.ts',
       './assets/ts/artplayer-plugin-multiple-subtitles.d.ts',
       './assets/ts/artplayer-plugin-vast.d.ts',
@@ -71,6 +70,7 @@
       './assets/ts/artplayer-plugin-websr.d.ts',
       './assets/ts/artplayer-proxy-canvas.d.ts',
       './assets/ts/artplayer-proxy-mediabunny.d.ts',
+      './assets/ts/artplayer-tool-iframe.d.ts',
       './assets/ts/artplayer.d.ts',
     ]