[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/suspendConversion/basicSuspendConversionForCallableReference.fir.kt

@@ -14,5 +14,5 @@ fun test() {
     foo2(42, ::bar2)
     foo2("str", ::bar2)
 
-    <!INAPPLICABLE_CANDIDATE!>foo2<!>(42, ::bar1)
+    <!INAPPLICABLE_CANDIDATE!>foo2<!>(42, <!UNRESOLVED_REFERENCE!>::bar1<!>)
 }

compiler/testData/diagnostics/tests/suspendConversion/suspendConversionWithReferenceAdaptation.fir.kt

@@ -16,6 +16,6 @@ fun all(s: String = ""): Int = 0
 fun test() {
     unitCoercion(::foo)
     defaults(::bar)
-    <!INAPPLICABLE_CANDIDATE!>varargs<!>(::baz)
+    <!INAPPLICABLE_CANDIDATE!>varargs<!>(<!UNRESOLVED_REFERENCE!>::baz<!>)
     unitCoercionAndDefaults(::all)
 }