[K/N][IR][optmz] Global analysis for top-level initializers

The analysis' goal is to remove redundant calls to initializers

kotlin-native/backend.native/tests/codegen/initializers/when1.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+// FILE: lib.kt
+val y = getY()
+
+private fun getY() = 42
+
+fun bar(x: Int) = x == 0
+
+// FILE: main.kt
+fun foo(x: Int) = when {
+    x > 0 -> 42
+    bar(x) -> 117
+    else -> -1
+}
+
+fun main() {
+    foo(123)
+    println(y)
+}