Completion of nested property of generic source property

Example Source class (Lombok used for brevity):
```java
import org.geolatte.geom.G2D;
import org.geolatte.geom.Point;

@Getter
@Setter
public class Location {
private Point coordinates;

// ...
}
```

eg. when attempting to map the latitude of `coordinates`:
```java
@Mapping(source = "coordinates.position.lat", target = "latitude")
```
[Point#getPosition()](https://javadoc.io/static/org.geolatte/geolatte-geom/1.4.0/org/geolatte/geom/Point.html#getPosition--) returns the type argument, in this case `G2D`, but the plugin infers it as `P` (the type parameter), and hence fails to autocomplete the [G2D#getLat()](https://javadoc.io/static/org.geolatte/geolatte-geom/1.4.0/org/geolatte/geom/G2D.html#getLat--) property.

Reproduce the nested mapping example with Location, Point, and coordinates.position.lat in IntelliJ IDEA. Start by tracing how the plugin resolves Point#getPosition() and its generic type argument, then verify autocomplete reaches G2D#getLat(). Done means the property is suggested as G2D rather than the unresolved type parameter P.

Written by the indexing model from the issue text.