Fix regression in wx version of FileEditor

[David-Baddeley]

File (and directory editors) are broken in current head (and the last couple of releases). See traceback below.

Traceback (most recent call last):
  File "/Users/david/dev/traitsui/traitsui/wx/file_editor.py", line 147, in show_file_dialog
    dlg = self._create_file_dialog()
  File "/Users/david/dev/traitsui/traitsui/wx/file_editor.py", line 209, in _create_file_dialog
    default_path=self._file_name.text(),
AttributeError: 'TextCtrl' object has no attribute 'text'

This looks like it can be traced to #1829, which seems to have copy-pasted the FileDialog creation code verbatim from the QT version into the wx version. Replacing the .text() call with the wx equivalent .GetValue() seems to fix things. Thought I'd submit a PR directly seeing as I had a simple fix, but happy to create an issue instead/as well if desired.

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[corranwebster]

Thanks for the contribution! This looks good to merge.

[greschd]

@corranwebster looking at the change in file_editor, I've noticed it also has a _get_value method:

traitsui/traitsui/wx/file_editor.py

Lines 234 to 239 in 86927f5

	def _get_value(self):
	"""Returns the current file name from the edit control."""
	if self.history is not None:
	return self.history.value
	return self._file_name.GetValue()

I'm wondering if that should be used instead? Or alternatively, if the _get_value method might be unused?

[corranwebster]

Possibly - _get_value matches the pattern for a Traits property getter, but that may be a coincidence. I'd need to dig in a bit, which I don't have time for right now - in the middle of getting Python 3.11 support working.