Fix transparency in toolbar buttons when not using comctl32.dll v6.

Old versions of comctl32.dll don't support alpha in the toolbar image list, so
use the masks only for them.

Closes #2609.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75785 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Allow using wxRearrangeList::Check() to change state programmatically.

Previous this resulted in an assert and broken behaviour as it didn't update
the internally stored state. Do update it now and remove the assert as it
isn't possible to distinguish between user code calling Check() and wxGTK
doing it itself from wxCheckListBox implementation.

Closes #15940.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75786 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add new XRC headers to the core project too.

Closes #15942.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75787 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775