Indexing a table by an enum's value

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### 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?

Diagnostics/Syntax Checking

### Expected Behaviour

Types defined with an enum as their key should be accessible via both the runtime enum itself and the value they represent.

### Actual Behaviour

A type defined with an enum as its key cannot be accessed with the enum's value.

### Reproduction steps

```
---@enum building_id
local building_id = {
ANY = -1,
ONE = 0,
TWO = 1,
}

---@type { [building_id]: { name: string } }
local building_attributes = {}

local anyName = building_attributes[building_id.ANY].name // Typed as "string"
local anyName = building_attributes[-1].name // Typed as "unknown"
```

### Additional Notes

### Discussed in https://github.com/LuaLS/lua-language-server/discussions/2402

### Log File

_No response_

Reproduce the diagnostics issue in the provided Lua example, beginning with enum key handling in the language server's type-checking path. Compare access through building_id.ANY with access through -1, and use the discussion linked in the issue for context; done means both forms resolve the table value as { name: string } rather than unknown.

Written by the indexing model from the issue text.