[JVM_IR] Fix stepping behavior for assignments to local variables.

compiler/testData/debug/stepping/variablesWithoutInitializer.kt

@@ -0,0 +1,29 @@
+// FILE: test.kt
+
+fun box() {
+    var x: String
+    var y: Int
+    var z: Boolean
+    z = false
+    y = 42
+    if (!z) {
+        x = y.toString()
+    }
+}
+
+// The JVM IR backend does not generate line number information for the
+// declaration of local variables without initializer. Stepping through
+// those does not seem useful. This is consistent with javac behavior
+// as well. The JVM backend does generate these line numbers.
+
+// LINENUMBERS
+// LINENUMBERS JVM
+// test.kt:4 box
+// test.kt:5 box
+// test.kt:6 box
+// LINENUMBERS
+// test.kt:7 box
+// test.kt:8 box
+// test.kt:9 box
+// test.kt:10 box
+// test.kt:12 box