Use consistent terminology between `IconGrid` and `ListBox` classes

[DanRStevens]

There are some subtle terminology variations between IconGrid and the ListBox classes, which we should probably resolve, so the API can be more consistent and easier to learn and use.

In particular, there is variation around the selection/selected term, particularly for getter/setter methods. This name choice affects:

• Index field names (mSelectedIndex)
• Getter/setter method names (setSelection, setSelected, selectedIndex)
• Event handler type aliases (SelectionChangedDelegate)
• Event handler field names (mSelectionChangedHandler)
• Event handler parameter names (selectionChangedHandler)
• Event handler method names (onListSelectionChange, onStructuresSelectionChange)

Additionally there is some variation with other Control related classes about the term Changed vs Change. Should it be selectionChangedHandler or selectionChangeHandler? Should event handler methods be named onSelectionChanged or onSelectionChange? There may be some other alternatives that are more suitable.