K2: add test confirming successful work of KT-56261

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/unused/localVariableInSecondaryConstructor.fir.txt

@@ -0,0 +1,19 @@
+FILE: localVariableInSecondaryConstructor.kt
+    public final fun main(): R|kotlin/Unit| {
+        lval localVariable: R|kotlin/Int| = Int(0)
+        local final class LocalClass : R|kotlin/Any| {
+            public constructor(arg: R|kotlin/Int|): R|LocalClass| {
+                super<R|kotlin/Any|>()
+            }
+
+            public final val arg: R|kotlin/Int| = R|<local>/arg|
+                public get(): R|kotlin/Int|
+
+            public constructor(): R|LocalClass| {
+                this<R|LocalClass|>(R|<local>/localVariable|)
+            }
+
+        }
+
+        R|/LocalClass.LocalClass|().R|<local>/arg|
+    }

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/unused/localVariableInSecondaryConstructor.kt

@@ -0,0 +1,10 @@
+fun main() {
+
+    val localVariable = 0
+
+    class LocalClass(val arg: Int) {
+        constructor() : this(localVariable)
+    }
+
+    LocalClass().arg
+}