HSEARCH-3885 Pass the inner predicate to the nested predicate builder…

… immediately

... instead of delaying until the call to toImplementation().
Because:

1. We no longer need this delay, like we did when the DSL was more
   complicated.
2. Removing this delay allows us to throw exceptions in the nested()
   method if the given predicate is not compatible with the nested
   predicate, leading to a clearer stacktrace for users.

engine/src/main/java/org/hibernate/search/engine/search/predicate/dsl/impl/NestedPredicateFieldStepImpl.java

@@ -51,6 +51,7 @@ public NestedPredicateOptionsStep<?> nest(SearchPredicate searchPredicate) {
 			throw log.cannotAddMultiplePredicatesToNestedPredicate();
 		}
 		this.childPredicateBuilder = builderFactory.toImplementation( searchPredicate );
+		builder.nested( childPredicateBuilder );
 		return this;
 	}
 
@@ -62,7 +63,6 @@ public NestedPredicateOptionsStep<?> nest(
 
 	@Override
 	protected B toImplementation() {
-		builder.nested( childPredicateBuilder );
 		return builder.toImplementation();
 	}