backend: improve typealias support:

* handle TypeAliasConstructorDescriptor in codegen
* ignore ignore typealias declaration in codegen

Also add test 'typealias1'.

backend.native/tests/build.gradle

@@ -143,6 +143,11 @@ task safe_cast(type: RunKonanTest) {
     source = "codegen/basics/safe_cast.kt"
 }
 
+task typealias1(type: RunKonanTest) {
+    goldValue = "42\n"
+    source = "codegen/basics/typealias1.kt"
+}
+
 task aritmetic(type: RunKonanTest) {
     source = "codegen/function/arithmetic.kt"
 }

backend.native/tests/codegen/basics/typealias1.kt

@@ -0,0 +1,6 @@
+fun main(args: Array<String>) {
+    println(Bar(42).x)
+}
+
+class Foo(val x: Int)
+typealias Bar = Foo