[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/multimodule/duplicateMethod/functionGenericsInParamsBoundsMismatch.fir.kt

@@ -1,40 +0,0 @@
-// !DIAGNOSTICS: -UNNECESSARY_SAFE_CALL
-
-// MODULE: m1
-// FILE: a.kt
-package p
-
-public interface B {
-    public fun <T> foo(a: T): B?
-}
-
-// MODULE: m2(m1)
-// FILE: b.kt
-package p
-
-public interface C : B {
-    override fun <T> foo(a: T): B?
-
-}
-
-// MODULE: m3
-// FILE: b.kt
-package p
-
-public interface Tr
-
-public interface B {
-    public fun <T: Tr?> foo(a: T): B?
-}
-
-// MODULE: m4(m3, m2)
-// FILE: c.kt
-import p.*
-
-fun test(b: B?) {
-    if (b is C) {
-        // hard to find parameters for an ambiguous call, so we rely on NONE_APPLICABLE here
-        // as opposed to diagnostics for a single unmatched candidate
-        b?.<!INAPPLICABLE_CANDIDATE!>foo<!>()
-    }
-}

compiler/testData/diagnostics/tests/multimodule/duplicateMethod/functionGenericsInParamsBoundsMismatch.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNNECESSARY_SAFE_CALL
 
 // MODULE: m1

compiler/testData/diagnostics/tests/multimodule/duplicateMethod/incompleteCodeNoNoneApplicable.fir.kt

@@ -16,5 +16,5 @@ import p.f
 
 fun test() {
     // There should be no "none applicable" error here
-    <!INAPPLICABLE_CANDIDATE!>f<!>(
+    <!NONE_APPLICABLE!>f<!>(
 <!SYNTAX!><!>}