[TIMOB-18062] iOS: AttributedString Parity with Android

Jira: https://jira.appcelerator.org/browse/TIMOB-18062

This PR is a continuation of https://github.com/appcelerator/titanium_mobile/pull/6409/ which came from #6358.

It addresses the comments by @pingwang2011 for the Android portion of the code. The doc is still not completed yet as Titanium.UI.iOS.Attribute and Titanium.UI.iOS.AttributedString yml files are missing the "deprecated".

The propertyAccessors is now used in AttributedStringProxy.java, AttributeProxy.java and LabelProxy.java.
https://github.com/appcelerator/titanium_mobile/pull/6409#discussion-diff-21472074

>From pingwang201:
>Add TiC.PROPERTY_ATTRIBUTE_RANGE to propertyAccessors. Those properties will be processed/changed in processProperties(KrollDict d) / handleCreationDict(KrollDict dict) and propertyChanged(String key, Object oldValue, Object newValue, KrollProxy proxy) / public void onPropertyChanged(String name, Object value). And you can get access to them using proxy.getProperty(String property) at any time.

TiC.PROPERTY_ATTRIBUTE_RANGE was added to propertyAccessors.