Use wxTE_RICH2 for in-place wxGrid text editor control.

Use wxTE_RICH2 for in-place wxGrid text editor control.

This works around a bug with the plain text edit control under MSW which seems
to totally lose its caret when we hide it and show it again for another cell.

This is not a proper fix for the problem, of course, but at least it does
allow to edit wxGrid cells in the meanwhile.

Closes #11681.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64646 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775