Added the TabbedMdiHost.MinTabExtent and MaxTabExtent properties that determine the size range of all tabbed MDI tabs.
Updated focus handling within the StandardSwitcher to better support screen readers.
Updated StandardSwitcher items to use document window filenames as UIA help text.
Changed the default value of AdvancedTabItem.CanClose to be true, which is more natural since that property combined with AdvancedTabControl.HasTabCloseButtons (already defaulted false) and CanTabsCloseOnMiddleClick (now defaults false) determines how the related features behave. These changes only affect standalone AdvancedTabControl usage.