K2: Support callable references adaptation on top-level

^KT-45989 In progress
^KT-54709 Related
^KT-55217 Fixed

compiler/testData/diagnostics/tests/callableReference/function/ambiguityTopLevelVsTopLevel.fir.kt

@@ -5,5 +5,5 @@ fun foo(x: Any, y: Int) = y
 fun main() {
     ::<!OVERLOAD_RESOLUTION_AMBIGUITY!>foo<!>
 
-    val fooRef: (Int, Any) -> Unit = ::<!UNRESOLVED_REFERENCE!>foo<!>
+    val fooRef: (Int, Any) -> Unit = ::foo
 }