Dragging a tab can show visual glitch when tab not fully visible (fixes #18733)

src/vs/workbench/browser/parts/editor/media/tabstitle.css

@@ -47,6 +47,10 @@
 	padding-left: 10px;
 }
 
+.monaco-workbench > .part.editor > .content > .one-editor-silo > .container > .title .tabs-container > .tab.dragged {
+	will-change: transform; /* forces tab to be drawn on a separate layer (fixes https://github.com/Microsoft/vscode/issues/18733) */
+}
+
 .monaco-workbench > .part.editor > .content > .one-editor-silo > .container > .title .tabs-container > .tab.close-button-left {
 	flex-direction: row-reverse;
 	padding-left: 0;

src/vs/workbench/browser/parts/editor/tabsTitleControl.ts

@@ -746,6 +746,10 @@ export class TabsTitleControl extends TitleControl {
 					e.dataTransfer.setData('DownloadURL', [MIME_BINARY, editor.getName(), resourceStr].join(':')); // enables support to drag a tab as file to desktop
 				}
 			}
+
+			// Fixes https://github.com/Microsoft/vscode/issues/18733
+			DOM.addClass(tab, 'dragged');
+			scheduleAtNextAnimationFrame(() => DOM.removeClass(tab, 'dragged'));
 		}));
 
 		// We need to keep track of DRAG_ENTER and DRAG_LEAVE events because a tab is not just a div without children,