Fix wxToolBarBase::AdjustToolBitmapSize() for HiDPI on OS X

wxOSX's wxToolBar code uses toolbar size computed by
AdjustToolBitmapSize() to determine which of the builtin toolbar sizes
to use. Because AdjustToolBitmapSize() returned 2x the "logical" size,
it would always pick NSToolbarSizeModeRegular regardless of icon size,
resulting in differently-sized toolbar on HiDPI and low-DPI screens.
Use scaled size instead.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@78088 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775