[FE] Add clear warning about future changes about nullability of safe call with non nullable receiver

^KT-46860

compiler/fir/analysis-tests/testData/resolve/smartcasts/boundSmartcasts/boundSmartcasts.kt

@@ -69,8 +69,8 @@ fun test_6(d1: D) {
 }
 
 fun test_7(d1: D, d2: D) {
-    val a = d1<!UNNECESSARY_SAFE_CALL!>?.<!>any
-    val b = d2<!UNNECESSARY_SAFE_CALL!>?.<!>any
+    val a = <!SAFE_CALL_WILL_CHANGE_NULLABILITY!>d1<!UNNECESSARY_SAFE_CALL!>?.<!>any<!>
+    val b = <!SAFE_CALL_WILL_CHANGE_NULLABILITY!>d2<!UNNECESSARY_SAFE_CALL!>?.<!>any<!>
     a as A
     a.foo() // should be OK
     b as B