[JS BE] Support val in when subject

#KT-25014 Fixed

compiler/testData/codegen/box/when/whenSubjectVariable/ieee754EqualityWithSmartCast.kt

@@ -1,22 +1,32 @@
 // !LANGUAGE: +VariableDeclarationInWhenSubject +ProperIeee754Comparisons
 // IGNORE_BACKEND: JVM_IR
-// IGNORE_BACKEND: JS, JS_IR
+// IGNORE_BACKEND: JS_IR
 
 val az: Any = -0.0
 val afz: Any = -0.0f
 
 fun box(): String {
-    when (val y = az) {
+    val y = az
+    when (y) {
         !is Double -> throw AssertionError()
         0.0 -> {}
         else -> throw AssertionError()
     }
-
-    when (val y = afz) {
+    val yy = afz
+    when (yy) {
         !is Float -> throw AssertionError()
         0.0 -> {}
         else -> throw AssertionError()
     }
 
+    testDoubleAsUpperBound(-0.0)
+
     return "OK"
-}
+}
+
+fun <T: Double> testDoubleAsUpperBound(v: T): Boolean {
+    return when (val a = v*v) {
+        0.0 -> true
+        else -> throw AssertionError()
+    }
+}