Add a shortcut annotation for adding a `nil,string` return type to functions (`@error`)

Returning of errors from Lua functions is often done by returning nil + error message (nil,string):

---@return table
---@overload fun(): nil, string
local function doSomething()

but this syntax can get complex when function takes parameters, or has other overloads. An old solution from LDoc was to use a @error annotation - I propose to add something similar to LuaLS.

该 payload 没有指出 LuaLS 的文件、测试或入口点；首先阅读所链接的 LDoc 手册中 @error 的行为，并定位 LuaLS 的注解解析和返回类型处理。Done 应定义并测试 @error 如何表示参数化函数以及具有其他重载的函数的 nil,string 返回值。