[FIR2IR] Make convertAndActualize method the only entrypoint to fir2ir

Fir2Ir conversion consists of multiple steps with complex logic (like
  conversion of each module, actualization, plugins application, constant
  evaluation), and to ensure that they all are executed correctly it's
  convenient to have the single entry point for all this machinery

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/Fir2Ir.kt

@@ -40,7 +40,9 @@ import org.jetbrains.kotlin.ir.declarations.IrExternalPackageFragment
 import org.jetbrains.kotlin.ir.declarations.IrMemberWithContainerSource
 import org.jetbrains.kotlin.ir.objcinterop.IrObjCOverridabilityCondition
 import org.jetbrains.kotlin.ir.types.IrTypeSystemContextImpl
-import org.jetbrains.kotlin.ir.util.*
+import org.jetbrains.kotlin.ir.util.DelicateSymbolTableApi
+import org.jetbrains.kotlin.ir.util.SymbolTable
+import org.jetbrains.kotlin.ir.util.getPackageFragment
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
 import org.jetbrains.kotlin.library.isNativeStdlib
 import org.jetbrains.kotlin.library.metadata.KlibMetadataFactories
@@ -115,9 +117,9 @@ internal fun PhaseContext.fir2Ir(
             visibilityConverter = Fir2IrVisibilityConverter.Default,
             kotlinBuiltIns = builtInsModule ?: DefaultBuiltIns.Instance,
             actualizerTypeContextProvider = ::IrTypeSystemContextImpl,
-            fir2IrResultPostCompute = {
+            fir2IrResultPostCompute = { _, irOutput ->
                 // it's important to compare manglers before actualization, since IR will be actualized, while FIR won't
-                irModuleFragment.acceptVoid(
+                irOutput.irModuleFragment.acceptVoid(
                         ManglerChecker(
                                 KonanManglerIr,
                                 Ir2FirManglerAdapter(FirNativeKotlinMangler),