[Feature Request] Automatically overload with `__call` metamethod.

There is already custom behavior when __index is defined in a metatable, why not __call? You can manually define the overload, but then you have to define the signature twice.

---@overload fun(a: string, b: number): boolean
local foo = setmetatable({}, {
    ---@param a string
    ---@param b number
    ---@return boolean
    __call = function(a, b)
        return true;
    end
});

首先跟踪现有的、针对带有 __index 的元表的自动行为，然后将其与 issue 中的 __call 示例进行比较。完成标准是：无需重复 @overload 声明即可推断可调用元表的函数签名，并覆盖字符串和数字示例。