@alias comments aren't visible

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?

Linux

### What is the issue affecting?

Annotations, Hover

### Expected Behaviour

a comment to an alias type should be shown as regular comment to a parameter would be shown (at least if there is no comment to the @param annotation itself). The hover message should read:

```
function f(arg: string)
@param arg — comment from alias

Unused functions.Lua Diagnostics.(unused-function)
Unused local `f`.Lua Diagnostics.(unused-local)
```

### Actual Behaviour

the comment to the alias type isn't shown. the hover message is:

```
function f(arg: string)
Unused functions.Lua Diagnostics.(unused-function)
Unused local `f`.Lua Diagnostics.(unused-local)
```

### Reproduction steps

1. cat << EOF > file.lua
---@alias t_arg string comment from alias
---@param arg t_arg
local function f(arg)
end
EOF
2. code file.lua
3. hover over the function name and read message

使用所示的 @alias 和 @param 註解在 file.lua 中重現問題，然後檢查函式文件的 hover 進入點。完成標準是：將游標暫留在 f 上時包含作為 @param arg 的別名註解，同時保留現有診斷並遵循任何明確的 @param 註解。

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