Report virtual desktop switches in Windows 10 (#8259)
* Report virtual desktop switches in Windows 10.
The desktop is checked on focus changes, and also the desktop's own name changes in case the focus does not move (such as when on the task bar).
* eventHandler: desktop switches can only be reported on Windows 10 April 2019 and above.
* Update what's new.
* Fix winVersion check for virtual desktop switches.
* Desktop IAccessible NVDAObject: hardcode its role to window, and ensure that parent, next and previous are all None, so that it could be used for the root of the NVDAObject tree. Window NVDAObject: don't ban the desktop window class from using a higher API, which means it will no use IAccessible., and therefore on newer Windows 10 builds, the virtual desktop name will be reflected in the Desktop NVDAObject's name.
* Event handler: April 2019 -> May 2019 Update
* Update what's new.
