Refocus after Dialog close triggers Tab change

The DialogHost tries to "re-focus" the item previously selected. This is the code for it:
https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/blob/5533b50a6cff78cb75fbb52e16f7c9e06c62446c/MaterialDesignThemes.Wpf/DialogHost.cs#L268

This is very problematic, when the previous control was a TabItem, because Focus()ing a TabItem actually activates the respective tab.

Here is a very simple reproduction:

• Have a TabControl within a DialogHost
• Focus a given TabItem (i.e. by clicking on an already active Tab)
• In the SelectionChanging Event of the TabControl Show the Dialog (i.e. "Loading data ...")
• Click another Tab

The following happens:

• DialogHost remembers, that the first tab is currently focused
• The click on the second Tab activates this Tab
• Dialog is shown and closed again, after data is loaded
• Dialog calls Focus() on first tab
  => First tab will be selected again

I just created the issue as I'm not sure, what the best solution for this. My current feeling tells me to just check for if(!(dialogHost._restoreFocusDialogClose is TabItem), but there might be other elements, where a re-focus is not desired?

I'd be happy to provide a PR after we agree on a solution.

Also - for now, I'd welcome any idea for a good workaround I could place into the application to make it work for now.

从 DialogHost.cs 大约第 268 行开始，复现与 TabControl、TabItem 以及打开对话框的 SelectionChanging 处理程序之间的交互。调查对于选项卡项，是否应跳过将焦点恢复到之前选中的元素，或以不同方式处理，并验证关闭对话框后新选中的选项卡仍处于活动状态。