FxContainer fix to make sure partRemoved/partAdded are never called with a null instance. In this case, in clearSkinParts(), we would call partRemoved() on all parts, whether they were there or not. This was causing a Thermo bug.
ASDoc fixes for Group, FxContainer, and FxDataContainer. Removing content property from ASDocs...this is not the recommended way to add items/remove items to Group/FxContainer. You should use the addItem/removeItem APIs. This is consistent with Flash Player and Halo. Under the hood someone can still set the content array, but it's discouraged because you could set two Groups to the same content array, which is hard to detect. Also, made currentContentGroup in FxContainer mx_internal...this is an implementation detail for us and something we may change later on. I also added some other ASDoc cleanups and fixes.
QE Notes: Ran checkintests and Mustella tests for gumbo/core/ and gumbo/components/FxDataContainer. Joann is updatating the one test that failed. WHen verifying SDK-17750, please also verify Thermo bug SDK-17800.
Doc Notes: This change includes ASDoc changes
Bugs: SDK-17750, SDK-17741, SDK-17756