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/catch6.kt

@@ -0,0 +1,22 @@
+fun main(args : Array<String>) {
+
+    try {
+        println("Before")
+        foo()
+        println("After")
+    } catch (e: Exception) {
+        println("Caught Exception")
+    } catch (e: Error) {
+        println("Caught Error")
+    }
+
+    println("Done")
+}
+
+fun foo() {
+    try {
+        throw Error("Error happens")
+    } catch (e: Exception) {
+        println("Caught Exception")
+    }
+}