HSEARCH-4950 Update nested context checks

Author: marko-bekhta

backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/search/predicate/impl/AbstractElasticsearchNestablePredicate.java

@@ -35,7 +35,6 @@ public void checkNestableWithin(String expectedParentNestedPath) {
 
 	@Override
 	public JsonObject toJsonQuery(PredicateRequestContext context) {
-		checkNestableWithin( context.getNestedPath() );
 
 		List<String> nestedPathHierarchy = getNestedPathHierarchy();
 		String expectedNestedPath = nestedPathHierarchy.isEmpty()
@@ -44,6 +43,7 @@ public JsonObject toJsonQuery(PredicateRequestContext context) {
 
 		if ( Objects.equals( context.getNestedPath(), expectedNestedPath ) ) {
 			// Implicit nesting is not necessary
+			checkNestableWithin( context.getNestedPath() );
 			return super.toJsonQuery( context );
 		}
 
@@ -52,6 +52,7 @@ public JsonObject toJsonQuery(PredicateRequestContext context) {
 		// so that the predicate is actually executed in this context.
 		PredicateRequestContext contextAfterImplicitNesting =
 				context.withNestedPath( expectedNestedPath );
+		checkNestableWithin( expectedNestedPath );
 
 		JsonObject result = super.toJsonQuery( contextAfterImplicitNesting );
 

integrationtest/backend/tck/src/main/java/org/hibernate/search/integrationtest/backend/tck/search/predicate/KnnPredicateSpecificsIT.java

@@ -690,6 +690,10 @@ void insideOtherPredicate() {
 		@Test
 		@SuppressWarnings("unchecked")
 		void nestedVector() {
+			assumeTrue(
+					TckConfiguration.get().getBackendFeatures().supportsVectorSearchInsideOtherPredicates(),
+					"This test won't work on some backends that can only accept a knn predicate at top level."
+			);
 			assertThat(
 					indexNested.createScope().query()
 							.select( f -> f.composite()