Make hack for button creation in wxOSX more robust.

Make hack for button creation in wxOSX more robust.

Don't crash when creating a plain wxButton with wxBU_NOTEXT style. This
happened because we skipped creating the peer (real implementation) in this
case entirely on the assumption that we were creating a wxBitmapButton, but
this is not necessarily the case. So now test that the creation of the peer is
really disabled before skipping it (this required adding ShouldCreatePeer()
accessor).

Merging wxWidgetImpl::CreateButton() and CreateBitmapButton() (and the same
thing for toggle buttons) would still be a better solution but while it's
trivial to do for Cocoa, it isn't for Carbon. And we can't use a single
function for Cocoa but different functions for Carbon, so for now just
continue to use this hack.

Closes #13622.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72896 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775