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.

docs/assets/ts/artplayer.d.ts

@@ -1054,6 +1054,8 @@ export interface ComponentOption {
 
 
 
+export type { Config, Events, I18n, Icons, Option, Player, Setting, SettingOption, Subtitle, Template, Utils }
+
 export default class Artplayer extends Player {
   constructor(option: Option, readyCallback?: (this: Artplayer, art: Artplayer) => unknown)