How to make a third-party member function as deprecated

還沒有人認領這個 Issue。

### 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?

Diagnostics/Syntax Checking

### Expected Behaviour

```lua
---@deprecated
M.add = M.add
```
The left one should have marked as deprecated immediately when used such as ~u:add~

### Actual Behaviour

1. it not works first.
2. and works unexpectedly.

### Reproduction steps

1. Write the code
```lua
-- File A

---@class A
local A = {}

---@param attr string
function A.add(attr)
end

-- File B

---@class A
local B = A

---@deprecated
B.add = A.add

B.add('some attr')
```
We'll find that B.add havn't marked as deprecated
2. Keep write the followed
```lua
-- File C

---@class A
---@field add fun(attr: string)
local C = A
```

### Additional Notes

My original intention was to mark a third-party member function as deprecated.
As there was no straightforward way, I think, to do it, I had to use a lot of tricks, which led to more subsequent problems.

### Log File

_No response_

從 issue 中的 File A、File B 和 File C 重現開始，重點關注診斷在已棄用指派之後如何標記 B.add。在 Visual Studio Code 擴充功能中執行重現，並將觀察到的診斷與針對 B.add 的預期棄用警告進行比較。

由索引模型根據 Issue 內容生成。