Mark QtWebEngineProcess as compatible with Windows 10

This fixes ::GetVersionEx to report the actual Windows version,
instead of always reporting Windows 8. Note though that this
fixes only the renderer process - the manifest of the user process
is beyond our control.

Chromium currently uses the dynamic checks for Windows 10 to e.g.
enable advanced sandboxing for ppapi, and scroll performance
(see https://bugs.chromium.org/p/chromium/issues/detail?id=517183

)

Change-Id: I72870f31eac2074748b2c11a2b6cab9a03e62527
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>