Add support for drag and drop document attachment

[boswelja]

Describe the need of your request

We can attach images and documents in the chat window to pass along to models, but if I just downloaded an image for example, it's a little tedious having to open a picker and find where it was downloaded to.

Proposed solution

Support drag and drop in the chat window. Carrying on from the previous example, this would allow us to drag an image from our browser downloads straight into the chat window.

Additional context

No response