Support toString for AdaptedFunctionReference subclasses

Also make it serializable like other lambdas, suspend lambdas and normal
callable references.

compiler/testData/codegen/box/callableReference/adaptedReferences/toString.kt

@@ -0,0 +1,27 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND_FIR: JVM_IR
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+class A {
+    fun foo(s: String = "", vararg xs: Long): CharSequence = "foo"
+}
+
+fun check(expected: String, x: Any) {
+    assertEquals(expected, x.toString())
+}
+
+fun coercionToUnit(f: (A, String, LongArray) -> Unit): Any = f
+fun varargToElement(f: (A, String, Long, Long) -> CharSequence): Any = f
+fun defaultAndVararg(f: (A) -> CharSequence): Any = f
+fun allOfTheAbove(f: (A) -> Unit): Any = f
+
+fun box(): String {
+    check("Function3<A, java.lang.String, long[], kotlin.Unit>", coercionToUnit(A::foo))
+    check("Function4<A, java.lang.String, java.lang.Long, java.lang.Long, java.lang.CharSequence>", varargToElement(A::foo))
+    check("Function1<A, java.lang.CharSequence>", defaultAndVararg(A::foo))
+    check("Function1<A, kotlin.Unit>", allOfTheAbove(A::foo))
+
+    return "OK"
+}

compiler/testData/codegen/box/callableReference/serializability/adaptedReferences.kt

@@ -0,0 +1,36 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND_FIR: JVM_IR
+// WITH_REFLECT
+
+import java.io.*
+import kotlin.test.assertEquals
+
+class A {
+    fun foo(s: String = "", vararg xs: Long): String = "foo"
+}
+
+fun check(x: Any) {
+    val baos = ByteArrayOutputStream()
+    val oos = ObjectOutputStream(baos)
+    oos.writeObject(x)
+    oos.close()
+
+    val bais = ByteArrayInputStream(baos.toByteArray())
+    val ois = ObjectInputStream(bais)
+    assertEquals(x, ois.readObject())
+    ois.close()
+}
+
+fun coercionToUnit(f: (A, String, LongArray) -> Unit): Any = f
+fun varargToElement(f: (A, String, Long, Long) -> String): Any = f
+fun defaultAndVararg(f: (A) -> String): Any = f
+fun allOfTheAbove(f: (A) -> Unit): Any = f
+
+fun box(): String {
+    check(coercionToUnit(A::foo))
+    check(varargToElement(A::foo))
+    check(defaultAndVararg(A::foo))
+    check(allOfTheAbove(A::foo))
+
+    return "OK"
+}