Returning generics with `T<X, Y>`

还没有人认领这个 Issue。

Below, I have a generic list that uses fluid interface to return itself for some methods:

```lua
--- @class List
local List = {}

--- @generic T : List, V, _
--- @param self T
--- @param value V # Element value to insert
--- @return T # Returning itself (a generic)
function List:insert(value)
return self -- Returning itself (a generic)
end

-- test
---@type List
local mylist

local testingType = mylist:insert(1)
-- ^ Testing type is not `List` but literally `T`
```

**Expected behavior**
testingType is of type `List`

I am thinking that this case could be something to look at for the 3.0 update.

(Edit: perfect #1000th issue...)

payload 未指出源文件或测试。首先重现提供的 List:insert 示例，并将推断出的类型与预期的 List 进行比较；然后跟踪泛型返回类型推断，并添加一个回归测试，确认结果不再是字面量 T。

由索引模型根据 Issue 内容生成。