[FIR] Properly support smartcasts on stable when subjects in when conditions

^KT-49860 Fixed

compiler/testData/ir/irText/expressions/floatingPointComparisons/whenByFloatingPoint.fir.kt.txt

@@ -39,7 +39,7 @@ fun testSmartCastInWhenConditionInBranch(x: Any): Int {
     val tmp3_subject: Any = x
     when {
       tmp3_subject !is Double -> -1
-      EQEQ(arg0 = tmp3_subject, arg1 = 0.0) -> 0
+      ieee754equals(arg0 = tmp3_subject /*as Double */, arg1 = 0.0) -> 0
       else -> 1
     }
   }
@@ -77,3 +77,4 @@ fun testWithPrematureExitInConditionSubexpression(x: Any): Int {
     }
   }
 }
+