Introduce AdaptedFunctionReference runtime class

It's used as a superclass for anonymous classes for adapted function
references. Its main feature is that it _doesn't_ inherit from KFunction
(as opposed to FunctionReference), as per the decision to postpone
reflection support for adapted function references in KT-36024.

 #KT-36024 Fixed

compiler/testData/codegen/box/callableReference/equality/coercionToUnitWithDefaults.kt

@@ -1,4 +1,4 @@
-// IGNORE_BACKEND: JVM_IR, JS, JS_IR, NATIVE
+// IGNORE_BACKEND: JS, JS_IR, NATIVE
 // IGNORE_BACKEND_FIR: JVM_IR
 // FILE: test.kt