Don't ignore invalid files entered into wxFileDirPickerCtrlBase.

Don't ignore invalid files entered into wxFileDirPickerCtrlBase.

File/directory picker controls with wxFLP_FILE_MUST_EXIST/wxDIRP_DIR_MUST_EXIST
style simply ignored any value entered by user if it didn't correspond to an
existing file/directory. This meant that the program didn't use the value that
was shown on the screen resulting in very confusing UI -- e.g. a program could
complain that no value was entered when actually it was and just corresponded
to a non-existing file.

As we can't prevent the entry of arbitrary strings in the text field of the
file picker control, stop pretending that we can validate it and just update
the control value, and send the corresponding event, whenever the text control
value changes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72475 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775