@overload does not cooperate with @alias

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?

Annotations, Diagnostics/Syntax Checking

### Expected Behaviour

When I define an @alias, an @overload command should be able to use it.

### Actual Behaviour

I receive the error:
```
`fun` expected. Lua Syntax Check.(luadoc-miss-fun-after-overload)
```

### Reproduction steps

```
---@alias what fun():"ok"

---@class huh
---@overload what
local huh = {}
```

Start with the Lua documentation annotation handling for @alias and @overload, using the reproduction in the issue as the first case to run. Trace why @overload what produces the luadoc-miss-fun-after-overload diagnostic. Done means the alias-based overload is accepted without that diagnostic while existing overload syntax remains valid.

Written by the indexing model from the issue text.