[FIR2IR] Treat delegated functions as fake-overrides

Delegated callables in FIR are session-dependant (as fake-overrides),
  so it's incorrect to use their FIR as a key for declaration storage.
  Pair of original function and owner lookup tag should be used instead

^KT-62671 Fixed

compiler/testData/codegen/box/multiplatform/k2/defaultArguments/defaultArgumentInDelegatedFunction.kt

@@ -0,0 +1,24 @@
+// IGNORE_BACKEND_K1: JS, JS_IR, JS_IR_ES6, NATIVE, WASM
+// LANGUAGE: +MultiPlatformProjects
+// ISSUE: KT-62671
+
+// MODULE: common
+// FILE: common.kt
+interface A {
+    fun foo(x: Int = 1): String
+}
+
+class B : A  {
+    override fun foo(x: Int): String {
+        return if (x == 1) "OK" else "Fail: $x"
+    }
+}
+
+class X(val delegate: A = B()) : A by delegate
+
+// MODULE: platform()()(common)
+// FILE: platform.kt
+fun box(): String {
+    val x = X()
+    return x.foo()
+}