IR: Don't use IrStringConcatenation for ordinary toString calls

We can only use IrStrinConcatentation to represent calls to Any?.toString
and toString calls on primitive types. Otherwise, x.toString() and "$x"
are observably different when x is a non-null type with null value
(e.g., an @NotNull value coming from Java).

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -27846,6 +27846,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/strings/interpolation.kt");
         }
 
+        @TestMetadata("javaToStringNPE.kt")
+        public void testJavaToStringNPE() throws Exception {
+            runTest("compiler/testData/codegen/box/strings/javaToStringNPE.kt");
+        }
+
         @TestMetadata("kt2592.kt")
         public void testKt2592() throws Exception {
             runTest("compiler/testData/codegen/box/strings/kt2592.kt");