src/vs/workbench/browser/parts/editor/editorPart.ts/EditorPart/mergeAllGroups
class EditorPart:	mergeAllGroups(target = this.activeGroup): IEditorGroupView {
		for (const group of this.getGroups(GroupsOrder.MOST_RECENTLY_ACTIVE)) {
			if (group === target) {
				continue; // keep target
			}

			this.mergeGroup(group, target);
		}

		return target;
	}