Cannot inherit generic classes (including tables)

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Hello, I apologize for bringing yet another generics issue as I know it takes time for it to be made solid... Thanks for looking into my problem. I use the following code to extend the `number[]` class, but then the elements are not marked as numbers for a non literal object.
```lua
---@class NumberTable: number[]

---@param t NumberTable
---@return number|nil
function FirstElement(t)
local n = t[1] -- marked as unknown
return n
end

---@param t number[]
---@return number|nil
function FirstElementBis(t)
local n = t[1] -- marked as number
return n
end
```
I would expect `t[1]` to be marked as `number`. I also tried replacing `number[]` with `table` and `table` without success. Thank you!

(I use LuaLS on Neovim on Linux)

Reproduce the issue in LuaLS with the provided NumberTable and FirstElement annotations, using Neovim on Linux as described. Compare the inferred type of t[1] with the direct number[] case and the table variants. Done means inherited generic and table annotations consistently identify the element as number.

Written by the indexing model from the issue text.