Returning generics with `T<X, Y>`

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...)

The payload names no source file or test. Start by reproducing the provided List:insert example and compare the inferred type with the expected List; then trace generic return-type inference and add a regression test confirming the result is no longer the literal T.

Written by the indexing model from the issue text.