[Test] Save IR bytecode dumps from BytecodeListingHandler to .ir.txt file instead of _ir.txt

This is needed to keep consistency with other dumps and to allow
  test helper plugin to recognize those dumps

compiler/testData/codegen/bytecodeListing/localFunctions/simple.ir.txt

@@ -0,0 +1,6 @@
+@kotlin.Metadata
+public final class SimpleKt {
+    // source: 'simple.kt'
+    private final static method foo$bar(): void
+    public final static method foo(): void
+}