Subwindow issues on Windows

[arthmis]

This issue will have to wait on a few enhancements to druid.

One issue is that WindowLevel is not implemented for Windows 10. Creating subwindows on Windows 10 uses the platform::WindowBuilder::build function that is used to create app level windows. The issue is that this function treats all windows as overlapped windows. As a result dropdowns and other subwindows show up on the taskbar.

For modals, tooltips, and dropdowns they should be pop up windows I believe.

The last issue is creating a subwindow takes focus away the parent window which is fine depending on the type of subwindow. For something like a tooltip though, it shouldn't take away focus.

A small fix to make the popup windows not show up in the taskbar is to set their extended style to WS_EX_TOOLWINDOW. The other fix would be to wait on the work being done to embed child windows within an App window. On Windows 10, setting the parent handle for a popup window prevents the popup window from showing up on the taskbar.