[FIR] Bring equivalent call behavior closer to K1

#KT-61159 Fixed

compiler/testData/codegen/box/equivalentCalls/localEquivalentWins.kt

@@ -0,0 +1,13 @@
+// MODULE: lib
+// FILE: lib.kt
+val a = "FAIL 1"
+
+// MODULE: main(lib)
+// FILE: box.kt
+private val a = "OK"
+
+fun box(): String {
+    if (a != "OK") return a
+
+    return "OK"
+}