Moving DataGroup from item based lookup to an index based lookup. Also, we now cleanup old item renderers when the dataProvider changes. This solves some memory leak problems.
Because of this, we should now be able to deal with duplicate items again.
We still need to work on data collection changes in the virtual layout case.
QE Notes: Please add the tests for dup items back in
Doc Notes: -
Bugs: SDK-19245, SDK-18043
tests: checkintests, DataGroup and FxList mustella tests (some new ones failed, but are really due to SDK-19287, and these tests should be excluded to that bug now)