Append all items at once during wxChoice creation in wxMSW.

Append all items at once during wxChoice creation in wxMSW.

Appending all items at once is more efficient than doing it one by one in the
loop 9probably because of CB_INITSTORAGE that we send in this case).

Closes #13899.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70454 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775