Extension install from local zip files

[abose]

The drag-and-drop functionality for extension installation has been removed due to its limited usage and poor user experience. Previously, users had to navigate to the extension manager and drop a zip file into a specific area to install extensions, a process that was not very intuitive. Removed the code as it was too much code doing too little ux things, and it was broken anyway.

Proposed Alternatives for Future

1. Adopting a method similar to VSCode, we will change the extension file type from .zip to .phx to indicate it's an extension for our editor.
2. Instead of requiring a specific drop location, users will be able to drag and drop the extension file anywhere within the editor. Doing so will initiate the extension installation process.
3. Additionally, double-clicking the extension file from the native file explorer/finder will launch the editor and start the extension installation workflow.

related: https://github.com/phcode-dev/phoenix/pull/1154