[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-21476260

Removed method:
"public void handleCreationDict(KrollDict options)"

>From pingwang2011
> values!=null is unnecessary since you have checked instanceof. Here is a little strange, if you already casted it to Object[], it cannot be null. Anyway, please put the instanceof check at the very beginning.