Add drop feedback UX (#179434)

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

src/vs/editor/browser/widget/codeEditorWidget.ts

@@ -2242,7 +2242,7 @@ class EditorDecorationsCollection implements editorCommon.IEditorDecorationsColl
 		this.set([]);
 	}
 
-	public set(newDecorations: IModelDeltaDecoration[]): void {
+	public set(newDecorations: readonly IModelDeltaDecoration[]): string[] {
 		try {
 			this._isChangingDecorations = true;
 			this._editor.changeDecorations((accessor) => {
@@ -2251,6 +2251,7 @@ class EditorDecorationsCollection implements editorCommon.IEditorDecorationsColl
 		} finally {
 			this._isChangingDecorations = false;
 		}
+		return this._decorationIds;
 	}
 }