✨ Support files and folders to be dragged in externally into project navigator

[austincondiff]

Is your feature request related to a problem? Please describe.

Users cannot drag files and folders into the project navigator to more them into the project folder

Describe the solution you'd like

We should be able to drag files and folders from an external source such as Finder in the project navigator onto the desired folder to move the files and/or folders there.

Additional context

Prerequisites:

• ✨ Ability to drag and drop files and folders in the project navigator #1018

[RayZhao1998]

Do we need copy the files, or just move them?

In Finder, it just moves files. But in Xcode, it has many advanced options such as Create folder references and Copy items if needed.

[austincondiff]

Like Finder, we should move the items by default, hold option while dropping to copy.

[matthijseikelenboom]

Maybe I'm a bit late, because @RayZhao1998 has already made the PR, but looking at VSCode, when moving a file to the project explorer, it copies the file. And perhaps it's not clear to people that hold option while dropping to copy is possible, even in Finder. Maybe we should notify the user what happened, whether files are copied or moved. Or indicate it with an icon at the mouse pointer.

[austincondiff]

In Finder, if you ⌥ + drag a file, a plus icon appears next to the cursor indicating that it will copy the file. When letting go of ⌥, the + disappears, indicating it will move the file. We should do the same, but the question is, should we do the inverse and have option move the file defaulting to copy behavior OR should we do the exact thing Finder does? Maybe this can be configured?

[matthijseikelenboom]

Yeah I think it's fine to implement it the way Finder does now. But in the future it could become a point of discussion within the community. (Btw, I didn't know about the + at the cursor, I suppose I don't use it often enough.)