FIR checker: differentiate UNSAFE_CALL from INAPPLICABLE_CANDIDATE

To do so, inside the root cause of inapplicable candidate errors,
we will record expected/actual type of receiver, if any.
That will help identifying inapplicable calls on nullable receiver.

compiler/testData/diagnostics/tests/dataClasses/extensionComponentsOnNullable.fir.kt

@@ -8,7 +8,7 @@ operator fun <T> Data<T>.component2() = y
 fun foo(): Int {
     val d: Data<Int>? = null
     // An error must be here
-    val (<!INAPPLICABLE_CANDIDATE!>x<!>, <!INAPPLICABLE_CANDIDATE!>y<!>) = d
+    val (x, y) = <!COMPONENT_FUNCTION_ON_NULLABLE, COMPONENT_FUNCTION_ON_NULLABLE!>d<!>
     return x + y
 }
 
@@ -17,6 +17,6 @@ data class NormalData<T>(val x: T, val y: T)
 fun bar(): Int {
     val d: NormalData<Int>? = null
     // An error must be here
-    val (<!INAPPLICABLE_CANDIDATE!>x<!>, <!INAPPLICABLE_CANDIDATE!>y<!>) = d
+    val (x, y) = <!COMPONENT_FUNCTION_ON_NULLABLE, COMPONENT_FUNCTION_ON_NULLABLE!>d<!>
     return x + y
 }