Check unknown target properties in new `@Ignored` annotation

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.

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:

@Ignored(targets = { "a", "b" })

首先定位 MapstructTargetReference 以及 @Ignored 注解中对目标的处理。验证未知的简单目标、如 driver.name 这样的嵌套属性，以及包含多个目标的数组语法；当每个无效目标都被报告为编译错误时，即表示完成。