By default, [Bindable] accessors / variables are not usable with BindingUtils.bindProperty()

In application code, doing this:

``mx.binding.utils.BindingUtils.bindProperty(targethost, "targetmember", sourcehost, ["sourcemember"]);``

where ``sourcehost.sourcemember`` is ``[Bindable]`` (with or without event name) will not produce updates of ``targethost.targetmember``.

The reason is that with the default config .xml file, the ``metadata`` showing ``'Bindable'`` is not generated in the .js file, and ChangeWatcher is expecting that info:

```
mx.binding.utils.ChangeWatcher.watch()
-> mx.binding.utils.ChangeWatcher.reset()
--> mx.binding.utils.ChangeWatcher.getEvents()
---> mx.binding.BindabilityInfo.getCachedInfo(host).getChangeEvents(name);
----> (first looking at mx.binding.BindabilityInfo.childChangeEvents[childName], otherwise looking at accessors / variables)
----> mx.binding.BindabilityInfo.addBindabilityEvents()
-----> org.apache.royale.reflection.utils.filterForMetaTags(members, ['Bindable'])
-----> mx.binding.BindabilityInfo.addChangeEvents
------> (if found, uses "valueChange" event for default [Bindable], or custom event name if specified)
```

Under ``ROYALE_REFLECTION_INFO`` in the .js file, it wants to see something like this:

`` 'text': { type: 'String', access: 'readwrite', declaredBy: 'my.awesome.company.MyClass', metadata: function () { return [ { name: 'Bindable' } ]; }},``

but it's seeing only something like this:

`` 'text': { type: 'String', access: 'readwrite', declaredBy: 'my.awesome.company.MyClass'},``

The solution is to uncomment the relevant part of the config .xml file, or use the compiler option:

``-compiler.keep-as3-metadata=Bindable``

Where is this prominently documented to help poor application developers from spending hours to figure this out?

Locate the default config .xml file and the existing documentation for compiler options and ROYALE_REFLECTION_INFO metadata. Document prominently that BindingUtils.bindProperty() needs Bindable metadata retained, including the relevant config setting and -compiler.keep-as3-metadata=Bindable; done means application developers can find and follow this guidance.

Written by the indexing model from the issue text.