[JVM_IR] Fix inlining of callable references to extension methods.

Check directly that the referenced function is an extension
function instead of relying on the annotation on the type.

^ KT-47988 Fixed.

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java

@@ -2718,6 +2718,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/callableReference/kt46902.kt");
         }
 
+        @Test
+        @TestMetadata("kt47988.kt")
+        public void testKt47988() throws Exception {
+            runTest("compiler/testData/codegen/box/callableReference/kt47988.kt");
+        }
+
         @Test
         @TestMetadata("nested.kt")
         public void testNested() throws Exception {