[FIR] Prevent replacing UNNECESSARY_SAFE_CALL with UNEXPECTED_SAFE_CALL

UNNECESSARY_SAFE_CALL is a warning,
UNEXPECTED_SAFE_CALL is an error, thus
it's a breaking change.

Also see KT-60695.

^KT-59860 Fixed


Merge-request: KT-MR-11210
Merged-by: Nikolay Lunyak <Nikolay.Lunyak@jetbrains.com>

compiler/testData/diagnostics/tests/unexpectedSafeCall.kt

@@ -0,0 +1,8 @@
+// FIR_IDENTICAL
+// DIAGNOSTICS: -ASSIGNED_BUT_NEVER_ACCESSED_VARIABLE
+// ISSUE: KT-59860
+
+fun test() {
+    val b: Int
+    run { b = 1 }<!UNNECESSARY_SAFE_CALL!>?.<!>let {} // K1: UNNECESSARY_SAFE_CALL, K2: UNEXPECTED_SAFE_CALL
+}