Generic attribute constraint doesn't work

Nobody has claimed this yet.

### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

Windows

### What is the issue affecting?

Type Checking, Completion

### Expected Behaviour

When using the `@generic` attribute on a method (`---@generic T : ClassA`) and I have a parameter as type T (`---@param item T The item`), when I hover over that `item` parameter I would expect it to list all fields in ClassA

### Actual Behaviour

It doesn't list the constrained type's fields. I just see the hover tooltip say: `(parameter) item: `, but none of ClassA's fields are shown

### Reproduction steps

Use this code:
```
---@class ClassA
---@field Name string
---@field Thing string
local ClassA = { Name = "name here", Thing = "thingy"}

---Adds an item
---@generic T: ClassA
---@param item T the Item
function ClassA:AddChild(item)
end
```
And hover over the `item` parameter on `AddChild`, and it won't show any of the fields of ClassA

### Additional Notes

_No response_

### Log File

_No response_

Start by reproducing the issue with the ClassA/AddChild example and hovering over the item parameter. Trace the generic constraint handling used by type checking and completion, then verify that the hover result exposes ClassA's Name and Thing fields for T and still reports the constrained type correctly.

Written by the indexing model from the issue text.