[K2, MPP] Remove redundant expect declarations from klib metadata

^KT-57250 Fixed

Introduce flat Fir2IrActualizedResult

It contains output from Fir2Ir and IrActualizer

compiler/testData/codegen/box/multiplatform/k2/basic/removeExpectDeclarationsFromMetadata.kt

@@ -0,0 +1,37 @@
+// IGNORE_BACKEND_K1: JVM, JVM_IR, JS, JS_IR, JS_IR_ES6, NATIVE, WASM
+// ISSUE: KT-57250
+// WITH_STDLIB
+// !OPT_IN: kotlin.ExperimentalMultiplatform
+// !LANGUAGE: +MultiPlatformProjects
+
+// MODULE: common
+// TARGET_PLATFORM: Common
+// FILE: common.kt
+
+expect class C()
+
+@OptionalExpectation
+expect annotation class WithActual(val x: Int)
+
+@OptionalExpectation
+expect annotation class WithoutActual(val s: String)
+
+expect fun k(): String
+
+// MODULE: platform()()(common)
+// FILE: lib.kt
+
+actual class C {
+    fun o() = "O"
+}
+
+actual annotation class WithActual(actual val x: Int)
+
+actual fun k() = "K"
+
+// MODULE: main(platform)
+// FILE: main.kt
+
+@WithActual(42)
+@WithoutActual("OK")
+fun box() = C().o() + k()