Windows: HKCU mutation lock depends on %AppData% #552

Follow-up from #502.

User-level installs on Windows serialize HKCU registry changes with a lock under %AppData%.
Two dbc processes with different %AppData% values therefore use separate locks while writing the same HKCU\SOFTWARE\ADBC\Drivers key.

The lock identity should come from the HKCU user/hive (e.g. the user SID) instead of %AppData%.