[FIR] Add test cases to prove resolution of backlog tickets

^KT-41728 Fixed
^KT-46586 Fixed
^KT-49696 Fixed
^KT-51160 Fixed
^KT-53308 Fixed

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/smartCastAfterDeadCode.fir.kt

@@ -0,0 +1,10 @@
+// WITH_STDLIB
+// ISSUE: KT-41728
+
+fun foo(a: String?) {
+    if (a == null) {
+        return
+        <!UNREACHABLE_CODE!>"hi".length<!>
+    }
+    a.length
+}

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/smartCastAfterDeadCode.kt

@@ -0,0 +1,10 @@
+// WITH_STDLIB
+// ISSUE: KT-41728
+
+fun foo(a: String?) {
+    if (a == null) {
+        return
+        <!UNREACHABLE_CODE!>"hi".length<!>
+    }
+    a<!UNSAFE_CALL!>.<!>length
+}

compiler/testData/diagnostics/tests/controlFlowAnalysis/reassignmentWithLambda.fir.kt

@@ -0,0 +1,21 @@
+// WITH_STDLIB
+// ISSUE: KT-49696
+
+interface Listener {
+    fun added(item: Any)
+    fun removed(item: Any)
+}
+
+val listeners = mutableListOf<Listener>()
+
+fun smartCast(item: Any?) {
+    var current = item
+    if (current == null) {
+        current = Any()
+        listeners.forEach { it.added(current) }
+    } else {
+        listeners.forEach { it.removed(current) }
+        current = Any()
+        listeners.forEach { it.added(current) }
+    }
+}

compiler/testData/diagnostics/tests/controlFlowAnalysis/reassignmentWithLambda.kt

@@ -0,0 +1,21 @@
+// WITH_STDLIB
+// ISSUE: KT-49696
+
+interface Listener {
+    fun added(item: Any)
+    fun removed(item: Any)
+}
+
+val listeners = mutableListOf<Listener>()
+
+fun smartCast(item: Any?) {
+    var current = item
+    if (current == null) {
+        current = Any()
+        listeners.forEach { it.added(<!SMARTCAST_IMPOSSIBLE!>current<!>) }
+    } else {
+        listeners.forEach { it.removed(<!SMARTCAST_IMPOSSIBLE!>current<!>) }
+        current = Any()
+        listeners.forEach { it.added(<!DEBUG_INFO_SMARTCAST!>current<!>) }
+    }
+}