Remove legacy JVM-specific file system, shell, and related implementations; migrate to platform-agnostic and common main modules.

src/commonMain/kotlin/mtmc/emulator/RewindStep.kt

@@ -0,0 +1,15 @@
+package mtmc.emulator
+
+import mtmc.util.Runnable
+
+class RewindStep {
+  var subSteps: MutableList<Runnable?> = ArrayList<Runnable?>()
+
+  fun rewind() {
+    subSteps.reversed().forEach({ obj: Runnable? -> obj!!.invoke() })
+  }
+
+  fun addSubStep(subStep: Runnable?) {
+    subSteps.add(subStep)
+  }
+}