Add test for smart cast on a value bound to when subject variable

E.g.:
  when (val y = x?.foo()) {
    null -> ...
    else -> ... // 'x' is also non-null here
  }

compiler/testData/diagnostics/tests/when/withSubjectVariable/smartCastOnValueBoundToSubjectVariable.kt

@@ -0,0 +1,9 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+
+fun foo(s1: String, s2: String) = s1 + s2
+
+fun test(x: Any?) =
+        when (val y = x?.toString()) {
+            null -> "null"
+            else -> foo(<!DEBUG_INFO_SMARTCAST!>x<!>.toString(), <!DEBUG_INFO_SMARTCAST!>y<!>)
+        }

compiler/testData/diagnostics/tests/when/withSubjectVariable/smartCastOnValueBoundToSubjectVariable.txt

@@ -0,0 +1,4 @@
+package
+
+public fun foo(/*0*/ s1: kotlin.String, /*1*/ s2: kotlin.String): kotlin.String
+public fun test(/*0*/ x: kotlin.Any?): kotlin.String

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -22484,6 +22484,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("smartCastOnValueBoundToSubjectVariable.kt")
+                public void testSmartCastOnValueBoundToSubjectVariable() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/withSubjectVariable/smartCastOnValueBoundToSubjectVariable.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("smartCastsOnSubjectVariable.kt")
                 public void testSmartCastsOnSubjectVariable() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/withSubjectVariable/smartCastsOnSubjectVariable.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -22484,6 +22484,12 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     doTest(fileName);
                 }
 
+                @TestMetadata("smartCastOnValueBoundToSubjectVariable.kt")
+                public void testSmartCastOnValueBoundToSubjectVariable() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/withSubjectVariable/smartCastOnValueBoundToSubjectVariable.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("smartCastsOnSubjectVariable.kt")
                 public void testSmartCastsOnSubjectVariable() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/withSubjectVariable/smartCastsOnSubjectVariable.kt");