This adds ability to the assistant panel's context editor to accept
files being dropped on it.
Multiple things can be dropped on the assistant panel:
- project panel entries (one or many)
- tabs (one)
- external files (one or many)
Release Notes:
- N/A
Demo:
https://github.com/user-attachments/assets/fddee751-cbdf-4e2c-ac80-35dfb857cc8a
Co-authored-by: Bennet <bennet@zed.dev>