[FE 1.0] Prohibit using non exhaustive if and when in rhs of elvis expression

^KT-44705
^KT-49349 Fixed

compiler/testData/diagnostics/tests/smartCasts/loops/elvisIfBreakInsideWhileTrue.kt

@@ -1,6 +1,6 @@
 public fun foo(x: String?, y: String?): Int {
     while (true) {
-        x ?: if (y == null) break
+        x ?: <!INVALID_IF_AS_EXPRESSION_WARNING!>if<!> (y == null) break
         // y is nullable if x != null
         y<!UNSAFE_CALL!>.<!>length
     }