Drag and Drop editors and tabs

[bpasero]

• win - @stevencl
• mac - @egamma
• linux - @chrmarti

Drag and drop for editors has been rewritten and needs testing across platforms. You can now

• drop into any opened tab in the title area
• drop to the empty space of the title area
• drop into the editor area (left, center, right)

Verify

• you can reorder and move tabs via DND and you see feedback
• you can open 1-N files at a specific position by dragging from outside VS Code (explorer, finder) into VS Code
• you can open a file or editor from the opened editor view or explorer by dragging
• you can open an editor to the side of an existing one by dragging towards the left or right area of an editor (this works for dragging from outside VS Code, dragging a tab or from the explorer)