[JVM_IR] Set correct origin for new variables on MFVC flattening.

Preserve information that variable is temporary while flattening.
Otherwise, unnecessary bytecode for them might be generated.

compiler/testData/codegen/box/valueClasses/inlineFunctions.kt

@@ -1,6 +1,5 @@
 // LANGUAGE: +ValueClasses
 // TARGET_BACKEND: JVM_IR
-// IGNORE_INLINER: IR
 // CHECK_BYTECODE_LISTING
 // WITH_STDLIB
 // CHECK_BYTECODE_TEXT