Make wxTextEntry::SetHint() work with all derived controls in wxOSX.

Previously, the method was only implemented in wxTextCtrl even though it used
wxTextEntry code to do the actual work. Move the implementation into
wxTextEntry.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75122 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775