Placing widgets on other widgets doesn't work as expected.

[cameron-toy]

Describe the bug

Placing a widget on another causes the placed widget to be placed oddly.

To Reproduce

Drag a dashboard output on top of another.

Expected behavior

The placed widget overlaps the underlying widget, moves the underlying widget to fit, or snaps to the outer edge of the underlying widget (still figuring out which is best).

Screenshots/gifs

Context

• OS: macOS 10.15.5
• Browser: Safari 13.1.1
• JupyterLab Version: 2.1.4

Addition info

The bug seems to be due to the offset position of the mouse event being from the underlying widget instead of the dashboard.