High DPI support didn't work for wxMDIParentFrame (and everything
inside it) because it was only enabled when InheritAttributes() from
wxNonOwnedWindow was called and this was only done in wxTopLevelWindow
but not in this class.
Fix this by removing the need to call InheritAttributes() at all and
just initializing m_perMonitorDPIaware when the window is created
automatically, to ensure that it can't be forgotten.
Co-Authored-By: Maarten Bent <MaartenBent@users.noreply.github.com>
Closes#22116.
00bd8c5576