Add wxDataViewRendererBase::GetEffectiveAlignment() and use it.

This helper method falls back on the alignment of the column if the renderer
alignment is not specified. This is almost always what should be used instead
of GetAlignment() to determine the alignment that really should be used in the
drawing code.

In particular, using GetEffectiveAlignment() in wxDataViewCustomRenderer fixes
the problem with bitmap columns ignoring column alignment for their bitmaps.

Closes #15498.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74825 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Use mask when drawing bitmaps in generic wxDataViewCtrl.

This allows to have bitmaps with transparent areas in them.

Closes #15510.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74826 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix assorted typos in comments and other non-code.

Closes #15509.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74827 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775