FIR: Report UNSAFE_INFIX_CALL for all infix-style calls, even if the

candidate is not an infix function.

This mirrors FE 1.0 (see
`AbstractTracingStrategy.reportUnsafeCallOnBinaryExpression()`) and
allows consistent handling for quickfixes on infix calls.

idea/testData/quickfix/nullables/unsafeInfixCall/unsafeInfixCall.kt

@@ -1,6 +1,4 @@
 // "Replace with safe (?.) call" "true"
 fun test(a : Int?) : Int? {
     return a <caret>compareTo 6;
-}
-
-/* IGNORE_FIR */
+}

idea/testData/quickfix/nullables/unsafeInfixCall/unsafeInfixCall.kt.after

@@ -1,6 +1,4 @@
 // "Replace with safe (?.) call" "true"
 fun test(a : Int?) : Int? {
     return a?.compareTo(6);
-}
-
-/* IGNORE_FIR */
+}