IC: Fix regression in detecting constants in KotlinClassInfo.kt

A constant is a static final field with non-null value. In a previous
commit (0b09be7), we accidentally removed the *non-null value*
filter when looking for constants in the bytecode.

This commit re-adds that filter to make sure the detection is correct.

Test: Added KotlinOnlyClasspathChangesComputerTest.testDelegatedProperties

^KT-58986: Fixed

compiler/incremental-compilation-impl/test/org/jetbrains/kotlin/incremental/classpathDiff/ClasspathChangesComputerTest.kt

@@ -290,6 +290,19 @@ class KotlinOnlyClasspathChangesComputerTest : ClasspathChangesComputerTest() {
         ).assertEquals(changes)
     }
 
+    /** Regression test for KT-58986.*/
+    @Test
+    fun testDelegatedProperties() {
+        // Check that classpath changes computation doesn't fail
+        val changes = computeClasspathChanges(File(testDataDir, "KotlinOnly/testDelegatedProperties/src"), tmpDir)
+        Changes(
+            lookupSymbols = setOf(
+                LookupSymbol(name = "delegatedProperty", scope = "com.example"),
+            ),
+            fqNames = setOf("com.example")
+        ).assertEquals(changes)
+    }
+
     /** Tests [SupertypesInheritorsImpact]. */
     @Test
     override fun testImpactComputation_SupertypesInheritors() {