Document Insert() and Prepend() overloads taking wxMenu.

Document these methods in addition to AppendSubMenu().

Closes #16052.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76091 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Make stretchable spacers work in vertical toolbars too in wxMSW.

Replace the old implementation of stretchable spacers based on changing the
size of the separators used as spacers as the toolbar size itself changed with
a new one, simply replacing the old separator with the new one of the correct
size, as it also works for the vertical toolbars, unlike the old approach.

Closes #13673.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76092 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775