Source value mapped more than once inspection for @ValueMapping

还没有人认领这个 Issue。

For value mappings a source value can only be mapped once. For example
```
import org.mapstruct.Mapper;
import org.mapstruct.ValueMapping;

@Mapper
public interface ValueMapper {

enum A {
A,B
}

enum B {
A,B
}

@ValueMapping(source = "A", target = "B")
@ValueMapping(source = "A", target = "A")
A from(B b);
}
```
is invalide as source `A` is mapped twice. MapStruct report this as

> Source value mapping: "A" cannot be mapped more than once.

Currently the plugin does not recognize this as an error. An inspection should be added for this.

For normal mappings there is already an inspection implemented and could be used as an example: https://github.com/mapstruct/mapstruct-idea/blob/main/src/main/java/org/mapstruct/intellij/inspection/TargetPropertyMappedMoreThanOnceInspection.java.

从 src/main/java/org/mapstruct/intellij/inspection/TargetPropertyMappedMoreThanOnceInspection.java 开始，该文件提供了现有的 inspection 模式。跟踪它如何检测重复的普通映射，然后对 @ValueMapping 源值采用相同的方法。完成的标准是能够识别重复的源值，并使用预期的错误消息进行报告。

由索引模型根据 Issue 内容生成。