Using LuaJIT's nil-coalescing extension does not narrow the type correctly

還沒有人認領這個 Issue。

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

Other

### Which OS are you using?

Linux

### What is the issue affecting?

Type Checking

### Expected Behaviour

Using the nil-coalescing operator should narrow an expressions type. For example, in this sample code, the type of `b` should be narrowed to `integer`:
```lua
---@type integer?
local foo = 1
local bar = foo ?? 2
```

### Actual Behaviour

Instead of the type being narrowed, the type of `foo` is copied instead, and the type of `bar` is thought to be `integer?` instead of `integer`.

### Reproduction steps

1. Insert the following sample code in a project:
```lua
---@type integer?
local foo = 1
local bar = foo ?? 2
```
2. Check the type of `b`

### Additional Notes

This seems to work fine using the classic Lua approach with `or`:
```lua
---@type integer?
local foo = 1
local bar = foo or 2
```
The type of `bar` is `integer` here, as expected.

### Log File

_No response_

首先，使用提供的 `??` 範例在 lua-language-server 型別檢查器中重現此問題，然後將其推論出的型別與等效 `or` 運算式的型別進行比較。追蹤 nil-coalescing 運算式如何處理 nullable 運算元；當 `bar` 被推論為 `integer` 且現有行為對比較情況仍然正確時，即表示完成。

由索引模型根據 Issue 內容生成。