feat: make IHTMLDataProvider async
          #199
        
          
      
                
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A common requirement is to send requests to the TS server to fetch tags, attributes or values. However, the current APIs do not support asynchronous operations, which forces us to use a quite dirty way to fetch asynchronous data:
https://github.com/vuejs/language-tools/blob/5ae4b381de01e3e9c0723fd4c5a74c1cbcc6ba78/packages/language-service/lib/plugins/vue-template.ts#L507-L522
https://github.com/vuejs/language-tools/blob/5ae4b381de01e3e9c0723fd4c5a74c1cbcc6ba78/packages/language-service/lib/plugins/vue-template.ts#L170-L185
This PR makes
provideTags,provideAttributesandprovideValuesasynchronous, while also causing many other APIs to become asynchronous.