Report warning on unused entities that can be renamed to _

Currently it's all about lambda parameters/destructuring entries

 #KT-14347 In Progress

compiler/testData/diagnostics/tests/inference/dependantOnVarianceNullable.kt

@@ -5,10 +5,10 @@ import java.util.*
 import java.util.Collections.*
 
 fun foo(list: List<String>) : String {
-    val w : String = max(list, comparator<String?> {o1, o2 -> 1
+    val w : String = max(list, comparator<String?> {<!UNUSED_PARAMETER!>o1<!>, <!UNUSED_PARAMETER!>o2<!> -> 1
     })
     return w
 }
 
 //from library
-fun <T> comparator(<!UNUSED_PARAMETER!>fn<!>: (T,T) -> Int): Comparator<T> {<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
+fun <T> comparator(<!UNUSED_PARAMETER!>fn<!>: (T,T) -> Int): Comparator<T> {<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>