* Allow passing in a `DataTransferItem` to workspace edit
Fixes#175800
Allows you to pass a file `DataTransferItem` to `WorkspaceEdit.createFile`. This lets us avoid transferring the data back and forth to the extension host, and also avoid having to base64 encode and decode it, significantly improving performance for large files
* Take data transfer file instead of data transfer item
For #179430
Adds two new UX components:
- An inline progress icon shown when a drop operation takes over 500ms. This replaces the notification. You can click on it to cancel the drop
- Post drop, a drop feedback icon that lets you drop the file in a different way. This lets you drop the file as plain text for instance instead of as a markdown link
* Revert "Revert "Add experimental setting to define where files should be copied for markdown (#169454)" (#169615)"
This reverts commit b2121c2dbe.
* Fix tests
These paths should always use `/`
