A union type should not merge class fields

Nessuno ha ancora preso questa issue.

### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

MacOS

### What is the issue affecting?

Annotations

### Expected Behaviour

```lua
---@class (exact) TypeA
---@field type 'A'
---@field commonField number
---@field specificFieldA number

---@class (exact) TypeB
---@field type 'B'
---@field commonField string
---@field specificFieldB string

---@alias Type_Either_A_Or_B_But_Not_Both TypeA|TypeB

---@type Type_Either_A_Or_B_But_Not_Both
local testA = {
type = 'A', --- Indicates that this should be of TypeA
commonField = 'test', --- Should be an error. TypeA.commonField should be a number
specificFieldA = 123, --- OK
specificFieldB = 'Hello' --- Should be an error. TypeA.specificFieldB doesn't exist
}

---@type Type_Either_A_Or_B_But_Not_Both
local testB = {
type = 'B', --- Indicates that this should be of TypeB
commonField = 'test', --- OK
specificFieldA = 123, --- Should be an error. TypeB.specificFieldA doesn't exist
specificFieldB = 'Hello' --- OK
}
```

### Actual Behaviour

`TypeA|TypeB` is merged, so none of the mismatched fields/types are reported as errors.

```
local testA: TypeA|TypeB {
commonField: string|number,
specificFieldA: number,
specificFieldB: string,
type: 'A'|'B',
}
```

### Reproduction steps

Paste the code into vscode

### Additional Notes

_No response_

### Log File

_No response_

Riproduci l'esempio annotato TypeA|TypeB nell'estensione Visual Studio Code, quindi traccia il modo in cui il language server unisce i campi delle classi union. Il lavoro è completato quando il discriminatore seleziona la classe corretta e segnala il campo comune non corrispondente commonField e i campi specifici dei membri mostrati nell'esempio.

Scritto dal modello di indicizzazione a partire dal testo della issue.