[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/nullabilityAndSmartCasts/InfixCallNullability.fir.kt

@@ -9,9 +9,9 @@ operator infix fun A.div(i : Int) {}
 operator infix fun A?.times(i : Int) {}
 
 fun test(x : Int?, a : A?) {
-    x.<!INAPPLICABLE_CANDIDATE!>plus<!>(1)
+    x.<!NONE_APPLICABLE!>plus<!>(1)
     x?.plus(1)
-    x <!INAPPLICABLE_CANDIDATE!>+<!> 1
+    x <!NONE_APPLICABLE!>+<!> 1
     <!INAPPLICABLE_CANDIDATE!>-<!>x
     x.<!INAPPLICABLE_CANDIDATE!>unaryMinus<!>()
     x?.unaryMinus()

compiler/testData/diagnostics/tests/nullabilityAndSmartCasts/NullableNothingIsExactlyNull.fir.kt

@@ -2,7 +2,7 @@ fun test() {
   val out : Int? = null
   val x : Nothing? = null
   if (out != x)
-    out.<!INAPPLICABLE_CANDIDATE!>plus<!>(1)
+    out.<!NONE_APPLICABLE!>plus<!>(1)
   if (out == x) return
-  out.<!INAPPLICABLE_CANDIDATE!>plus<!>(1)
+  out.<!NONE_APPLICABLE!>plus<!>(1)
 }

compiler/testData/diagnostics/tests/nullabilityAndSmartCasts/kt2216.fir.kt

@@ -16,7 +16,7 @@ fun foo() {
     val y: Int? = 0
     val z: Int? = 0
     <!INAPPLICABLE_CANDIDATE!>bar<!>(if (y != null) y else z, y)
-    y <!INAPPLICABLE_CANDIDATE!>+<!> 2
+    y <!NONE_APPLICABLE!>+<!> 2
     <!INAPPLICABLE_CANDIDATE!>baz<!>(y, y, if (y == null) return else y, y)
     baz(y, z!!, z, y)
 }

compiler/testData/diagnostics/tests/nullabilityAndSmartCasts/kt362.fir.kt

@@ -6,11 +6,11 @@ package example
 fun test() {
   val p = test.Public()
   if (p.public is Int) p.public + 1
-  if (p.<!INAPPLICABLE_CANDIDATE!>protected<!> is Int) p.<!INAPPLICABLE_CANDIDATE!>protected<!> + 1
+  if (p.<!HIDDEN!>protected<!> is Int) p.<!HIDDEN!>protected<!> <!NONE_APPLICABLE!>+<!> 1
   if (p.internal is Int) p.internal + 1
   val i = test.Internal()
   if (i.public is Int) i.public + 1
-  if (i.<!INAPPLICABLE_CANDIDATE!>protected<!> is Int) i.<!INAPPLICABLE_CANDIDATE!>protected<!> + 1
+  if (i.<!HIDDEN!>protected<!> is Int) i.<!HIDDEN!>protected<!> <!NONE_APPLICABLE!>+<!> 1
   if (i.internal is Int) i.internal + 1
 }
 

compiler/testData/diagnostics/tests/nullabilityAndSmartCasts/nullableReceiverWithOverloadedMethod.fir.kt

@@ -13,17 +13,17 @@ class B {
 
     fun f() {
         a = A()
-        a.<!INAPPLICABLE_CANDIDATE!>f<!>(true)
-        takeInt(a.<!INAPPLICABLE_CANDIDATE!>f<!>(""))
-        a.<!INAPPLICABLE_CANDIDATE!>f<!>()
+        a.<!NONE_APPLICABLE!>f<!>(true)
+        takeInt(a.<!NONE_APPLICABLE!>f<!>(""))
+        a.<!NONE_APPLICABLE!>f<!>()
     }
 
     fun g() {
         takeInt(if (3 > 2) {
             a = A()
-            a.<!INAPPLICABLE_CANDIDATE!>f<!>(true)
+            a.<!NONE_APPLICABLE!>f<!>(true)
         } else {
             6
         })
     }
-}
+}

compiler/testData/diagnostics/tests/nullabilityAndSmartCasts/unstableSmartcastWithOverloadedExtensions.fir.kt

@@ -9,6 +9,6 @@ var a: A? = null
 
 fun smartCastInterference(b: B) {
     if (a != null) {
-        a.<!INAPPLICABLE_CANDIDATE!>foo<!>(b)
+        a.<!NONE_APPLICABLE!>foo<!>(b)
     }
-}
+}