Android extensions: Do not cache ViewStub widgets, do not cast it automatically

plugins/android-compiler-plugin/testData/codegen/bytecodeShape/viewStub/viewStub.kt

@@ -0,0 +1,18 @@
+package test
+
+import android.app.Activity
+import android.os.Bundle
+import java.io.File
+import kotlinx.android.synthetic.main.layout.*
+
+public class MyActivity : Activity() {
+    fun test() {
+        stub
+    }
+}
+
+// 1 GETSTATIC test/R\$id\.stub
+// 0 INVOKEVIRTUAL test/MyActivity\._\$_findCachedViewById
+// 1 INVOKEVIRTUAL android/app/Activity\.findViewById
+// 0 CHECKCAST android/view/ViewStub
+// 2 CHECKCAST android/view/View