Support user-defined overridden native components

Users can override built-in components. Here are some findings. We should eventually support this.

Implementation in brighterscript:

• user-defined component with same name should "win". i.e. an overridden Button should now make roSGNodeButton point to the user's instance.
• If you need to reference the native one after overriding, then we should add a namespace that holds all these types (i.e. scenegraph.Button).

We have discovered that it is possible to override the native SceneGraph components by defining an XML component with the same name.

Questions:

Why does this work?

Is this intentional?

Could Roku please provide an official stance on whether this can be safely used or should never be used in our apps?

For example:

pkg:/components/Button.xml:

pkg:/components/MainScene.xml Screenshot of the above example:

• Cannot extend native component with same name.
  

Start by reproducing the override in pkg:/components/Button.xml and pkg:/components/MainScene.xml, then compare the behavior of the user-defined Button with the native SceneGraph component. The issue is done only when the supported behavior, native-component access, and compiler handling are clearly defined and covered by appropriate tests.