src/vs/workbench/services/editor/browser/editorService.ts/EditorService/findSideBySideGroup
class EditorService:	private findSideBySideGroup(): IEditorGroup {
		const direction = preferredSideBySideGroupDirection(this.configurationService);

		let neighbourGroup = this.editorGroupService.findGroup({ direction });
		if (!neighbourGroup) {
			neighbourGroup = this.editorGroupService.addGroup(this.editorGroupService.activeGroup, direction);
		}

		return neighbourGroup;
	}