feat(shares): add drag-n-drop option in the modal

[Antreesy]

☑️ Resolves

• Fix File drop is not possible when file modal is open #10883
• Logic is copied from

  spreed/src/components/ChatView.vue

  Lines 23 to 25 in f4d3343

  	@dragover.prevent="handleDragOver"
  	@dragleave.prevent="handleDragLeave"
  	@drop.prevent="handleDropFiles">

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

Style overview (when dragged over):

In action:

dragndrop.mp4

🏁 Checklist

• 🌏 Tested with Chrome, Firefox and Safari or should not be risky to browser differences
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required