[ExportAttributeTest] Use the read Bundle, not the original.

(Aside: rename the launch icon to "XA [Export] Demo" for eventually
better sample grouping.)

The original code read a Bundle from the Parcel, but didn't read from
that bundle. Consequently, deserialization logic was not fully tested,
introducing three related issues:

 1. The read Bundle instance doesn't have Bundle.ClassLoader set, and
    without the appropriate ClassLoader no types from the current
    package can be found. The result: a BadParcelableException [0].

 2. The MyParcel.CREATOR field must be public, otherwise a
    BadParcelableException is thrown [1].

 3. MySerializable must provide a
    MySerializable(IntPtr, JniHandleOwnership) constructor, as Java
    will create the instance without using the default constructor,
    resulting in a NotSupportedException/MissingMethodException [2].

[0]:
E/mono    (14301): Unhandled Exception:
E/mono    (14301): Android.OS.BadParcelableException: Exception of type 'Android.OS.BadParcelableException' was thrown.
E/mono    (14301): at Android.Runtime.JNIEnv.CallObjectMethod (intptr,intptr,Android.Runtime.JValue[]) <0x00080>
E/mono    (14301): at Android.OS.Bundle.GetSerializable (string) <0x0010b>
E/mono    (14301): at ExportAttributeTest.Activity1.MyButton_OnClick (Android.Views.View) <0x00173>
E/mono    (14301): at (wrapper dynamic-method) object.dynamic_callback_0 (intptr,intptr,intptr) <0x00077>
E/mono    (14301): at (wrapper native-to-managed) object.dynamic_callback_0 (intptr,intptr,intptr) <0x00047>
E/mono    (14301):
E/mono    (14301):   --- End of managed exception stack trace ---
E/mono    (14301): android.os.BadParcelableException: ClassNotFoundException when unmarshalling: exportattributetest.MyParcelable
E/mono    (14301):      at android.os.Parcel.readParcelable(Parcel.java:2077)
E/mono    (14301):      at android.os.Parcel.readValue(Parcel.java:1965)
E/mono    (14301):      at android.os.Parcel.readMapInternal(Parcel.java:2226)
E/mono    (14301):      at android.os.Bundle.unparcel(Bundle.java:223)
E/mono    (14301):      at android.os.Bundle.getSerializable(Bundle.java:1262)
E/mono    (14301):      at exportattributetest.Activity1.n_MyButton_OnClick(Native Method)

[1]:
E/mono    (13679): Unhandled Exception:
E/mono    (13679): Android.OS.BadParcelableException: Exception of type 'Android.OS.BadParcelableException' was thrown.
E/mono    (13679): at Android.Runtime.JNIEnv.CallIntMethod (intptr,intptr) <0x00070>
E/mono    (13679): at Android.OS.Bundle.Size () <0x0007f>
E/mono    (13679): at ExportAttributeTest.Activity1.MyButton_OnClick (Android.Views.View) <0x0039b>
E/mono    (13679): at ExportAttributeTest.Activity1.<OnCreate>m__0 (object,System.EventArgs) <0x00057>
E/mono    (13679): at Android.Views.View/IOnClickListenerImplementor.OnClick (Android.Views.View) <0x0005b>
E/mono    (13679): at Android.Views.View/IOnClickListenerInvoker.n_OnClick_Landroid_view_View_ (intptr,intptr,intptr) <0x0005b>
E/mono    (13679): at (wrapper dynamic-method) object.bf0d733e-ca75-4686-8110-e2b5a7aff538 (intptr,intptr,intptr) <0x00043>
E/mono    (13679):
E/mono    (13679):   --- End of managed exception stack trace ---
E/mono    (13679): android.os.BadParcelableException: Parcelable protocol requires a Parcelable.Creator object called  CREATOR on class xamtest.MyParcelable
E/mono    (13679):      at android.os.Parcel.readParcelable(Parcel.java:2086)
E/mono    (13679):      at android.os.Parcel.readValue(Parcel.java:1965)
E/mono    (13679):      at android.os.Parcel.readMapInternal(Parcel.java:2226)

[2]:
E/mono    (13938): Unhandled Exception:
E/mono    (13938): System.NotSupportedException: Unable to activate instance of type XamTest.MySerializable from native handle c6800021 ---> System.MissingMethodException: No
constructor found for XamTest.MySerializable::.ctor(System.IntPtr, Android.Runtime.JniHandleOwnership) ---> Java.Interop.JavaLocationException: Exception of type 'Java.Interop
.JavaLocationException' was thrown.
E/mono    (13938): Java.Lang.Error: Exception of type 'Java.Lang.Error' was thrown.
E/mono    (13938):
E/mono    (13938):   --- End of managed exception stack trace ---
E/mono    (13938): java.lang.Error: Java callstack:
E/mono    (13938):      at xamtest.MySerializable.n_ReadObjectDummy(Native Method)
E/mono    (13938):      at xamtest.MySerializable.readObject(MySerializable.java:38)
E/mono    (13938):      at java.lang.reflect.Method.invokeNative(Native Method)
E/mono    (13938):      at java.lang.reflect.Method.invoke(Method.java:511)
E/mono    (13938):      at java.io.ObjectInputStream.readObjectForClass(ObjectInputStream.java:1357)
E/mono    (13938):      at java.io.ObjectInputStream.readHierarchy(ObjectInputStream.java:1269)
E/mono    (13938):      at java.io.ObjectInputStream.readNewObject(ObjectInputStream.java:1858)