JVM_IR: use nullability when boxing/unboxing inline class types

Given inline class V(Any?), a coercion from (Object, V) to (Object, V?)
is boxing.

In theory, the same issue in the old backend can be fixed by making
`KotlinTypeMapper.mapUnderlyingTypeOfInlineClassType` use
`computeExpandedTypeForInlineClass`, but for some reason this breaks a
lot of stuff.

 #KT-48430 Fixed

compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -15222,6 +15222,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/inlineClasses/boxImplDoesNotExecuteInitBlock.kt");
         }
 
+        @TestMetadata("boxNullableForFakeOverride.kt")
+        public void testBoxNullableForFakeOverride() throws Exception {
+            runTest("compiler/testData/codegen/box/inlineClasses/boxNullableForFakeOverride.kt");
+        }
+
         @TestMetadata("boxNullableValueOfInlineClassWithNonNullUnderlyingType.kt")
         public void testBoxNullableValueOfInlineClassWithNonNullUnderlyingType() throws Exception {
             runTest("compiler/testData/codegen/box/inlineClasses/boxNullableValueOfInlineClassWithNonNullUnderlyingType.kt");