Avoid bogus focus loss event when wxTextCtrl is modified in wxOSX.

A wxEVT_KILL_FOCUS event was generated when wxTextCtrl::WriteText() was called
in wxOSX, even though the control didn't lose focus at all in this case. This
was completely unexpected and thoroughly confused wxGrid code which closed the
in place editor immediately after showing it because of this (this was perhaps
only the case since r68319 but the changes there were correct so they only
masked the real bug).

Avoid this bogus event by remembering the NSView currently being
programmatically modified and not doing anything in textDidEndEditing
notification if it is generated for this view.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68466 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775