How to make a third-party member function as deprecated

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### 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_

Start with the File A, File B, and File C reproduction in the issue, focusing on how the diagnostic marks B.add after the deprecated assignment. Run the reproduction in the Visual Studio Code extension and compare the observed diagnostics with the expected deprecation warning for B.add.

Written by the indexing model from the issue text.