Lombok's fluent accessors are discovered in builders, but not for getters

Nobody has claimed this yet.

### Expected behavior

Mapstruct is able to detect and map fluent properties back and forth when using lombok's `@Accessors(fluent = true)` annotation.

This was asked previously by someone in [this stackoverflow question](https://stackoverflow.com/questions/48724814/accessorsfluent-true-from-lombok-and-mapstruct-together) where @filiphr suggested writing a custom AccessorNamingStrategy, but I am unsure if this is still expected since mapstruct has since then added lombok and builders support.

### Actual behavior

Mapstruct errors with:
```
Error:(9, 5) java: No property named "fluentProp" exists in source parameter(s)...
```

### Steps to reproduce the problem

```java
@Value
@Builder
class Animal {

@Accessors(fluent = true)
boolean hasLegs;

}

@Value
@Builder
class Cat {

@Accessors(fluent = true)
boolean hasLegs;

}

@Mapper
public interface AnimalMapper {

@Mapping(target = "hasLegs", source = "hasLegs")
Cat toCat(Animal animal);

}
```

For this example, Mapstruct errors with:
```
Error:(9, 5) java: No property named "hasLegs" exists in source parameter(s). Type "Animal" has no properties.
```
It's interesting to note that hasLegs is detected correctly in the target since the builder accessors are always fluent, but just not in the source.

### MapStruct Version

1.5.5.Final

Start by locating the annotation processor's accessor-naming and Lombok/builder handling, then run the fluent @Accessors(fluent = true) reproduction shown in the issue. Done means MapStruct recognizes the source hasLegs property as well as the builder target and the Animal-to-Cat mapping compiles without the reported error.

Written by the indexing model from the issue text.