backend: add tests for try-catch-finally and throwing exceptions

also add some tests for bugs with unreachable code handling and variables

backend.native/tests/codegen/try/finally9.kt

@@ -0,0 +1,21 @@
+fun main(args : Array<String>) {
+    do {
+        try {
+            break
+        } finally {
+            println("Finally 1")
+        }
+    } while (false)
+
+    var stop = false
+    while (!stop) {
+        try {
+            stop = true
+            continue
+        } finally {
+            println("Finally 2")
+        }
+    }
+
+    println("After")
+}