JVM_IR fold safe calls and elvises

compiler/testData/codegen/box/safeCall/safeCallWithElvisFolding.kt

@@ -0,0 +1,8 @@
+fun String.foo(): String? = null
+
+fun test(a: String?, b: String?, c: String) =
+    a ?: b?.foo() ?: c
+// = (a ?: b?.boo()) ?: c
+// Here 'b?.foo()' returns null, which may break elvis semantics if we fold it carelessly.
+
+fun box() = test(null, "abc", "OK")