[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
-}
+}

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

@@ -14,8 +14,8 @@ class MyClass {
         var res = 0
         m = create()
         // See KT-7428
-        <!INAPPLICABLE_CANDIDATE, UNRESOLVED_REFERENCE, UNRESOLVED_REFERENCE!>for ((k, v) in m)
-            <!UNRESOLVED_REFERENCE!>res += (k.<!UNRESOLVED_REFERENCE!>length<!> + v.<!UNRESOLVED_REFERENCE!>length<!>)<!><!>
+        <!INAPPLICABLE_CANDIDATE!>for ((k, v) in m)
+            res += (k.length + v.length)<!>
         return res
     }
-}
+}

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

@@ -2,5 +2,5 @@
 fun foo(): Int {
     var i: Int? = 42
     i = null
-    return i <!INAPPLICABLE_CANDIDATE!>+<!> 1
-}
+    return i <!NONE_APPLICABLE!>+<!> 1
+}