src/vs/workbench/services/workingCopy/common/workingCopyEditorService.ts/WorkingCopyEditorService/isOpen
class WorkingCopyEditorService:	private isOpen(workingCopy: IWorkingCopy, editor: IEditorInput): boolean {
		for (const handler of this.handlers) {
			if (handler.handles(workingCopy) && handler.isOpen(workingCopy, editor)) {
				return true;
			}
		}

		return false;
	}