EditorInterface root div has select-none (user-select:none) applied globally
to prevent text selection during editing. Chrome/Safari refuse to start HTML5
drag-and-drop on elements that inherit user-select:none, which is why no
ghost image appeared, cursor never changed, and no dragstart events fired.
Fix: add select-text (user-select:text) to both draggable divs in
MediaThumbnail (list view and grid view). This overrides the inherited none
specifically on the elements that need to be dragged, without changing the
global UX behavior of the editor.
Zac Gaetano
5019563c38