Check unknown target properties in new `@Ignored` annotation

還沒有人認領這個 Issue。

Referencing a target that does not exist results in a compilation error.
Therefore we should support the check of target properties (`MapstructTargetReference`) for that annotation.

```java
interface FooMapper {

@Ignored(targets = "nonExistent") // mark this as unknown
CarDto map(Car car);
}
```

This should also work for nested properties like `@Ignored(targets = "driver.name")`.

Beware that writing it as an array must also work:
```java
@Ignored(targets = { "a", "b" })
```

首先定位 MapstructTargetReference 以及 @Ignored 註解中對目標的處理。驗證未知的簡單目標、如 driver.name 這樣的巢狀屬性，以及包含多個目標的陣列語法；當每個無效目標都被回報為編譯錯誤時，即表示完成。

由索引模型根據 Issue 內容生成。