[FIR] Improve diagnostic reporting & don't use error symbol for candidate if possible

Also introduce few new diagnostics:
- NONE_APPLICABLE more many inapplicable candidates
- HIDDEN for visible candidates

compiler/testData/diagnostics/tests/smartCasts/varnotnull/plusplusMinusminus.fir.kt

@@ -12,10 +12,10 @@ operator fun Long?.inc() = this?.let { it + 1 }
 fun bar(arg: Long?): Long {
     var i = arg
     if (i++ == 5L) {
-        return i<!INAPPLICABLE_CANDIDATE!>--<!> <!INAPPLICABLE_CANDIDATE!>+<!> i
+        return i<!INAPPLICABLE_CANDIDATE!>--<!> + i
     }
     if (i++ == 7L) {
-        return i++ <!INAPPLICABLE_CANDIDATE!>+<!> i
+        return i++ <!NONE_APPLICABLE!>+<!> i
     }
     return 0L
-}
+}