This is a heavily simplified version of Michael Müller's staging patch (the staging version got broken by the PE/Unix split)
I rebased that staging patch but I thought it was too big for what it does (so I did this instead)
As for automatically changing the status, SM_MEDIACENTER would require Windows version checks (which are never used in Wine) and SM_TABLETPC would likely require touchscreen/tablet detection (rbernon is working on some touch stuff so that could be useful)
-- v2: win32u: Enable the media center metric by default. win32u: Add registry key for changing tablet status.