open-file filetype field prevents filename Tab completion

Now that open-file uses inputMultiple in visidata v3.4, I can't use Tab to complete filenames, because Tab switches fields. Users will want filename completion more often than they'll need to specify a filetype, so I think we should figure out how the UI should allow completion.

For now, for users wanting Tab completion, you can edit your .visidatarc to restore the v3.3 definition of open-file by appending:

BaseSheet.addCommand('o', 'open-file', 'vd.push(openSource(inputFilename("open: "), create=True))', 'Open file or URL')

EDIT: To disable the filetype field more broadly (for commands like save-sheet, copy-selected, extract-* as well as open-file) put in the .visidatarc:

# for visidata v3.4.0: workaround to enable file completion and disable the filetype field
@VisiData.api
def inputPath(vd, *args, filetype='', **kwargs):
    'Input a path, ignoring the filetype field to work around a UI problem in visidata 3.4.0.'
    if args:
        prompt = args[0]
        args = args[1:]
    else:
        prompt = kwargs.pop('prompt', 'path: ')
    return Path(vd.inputFilename(prompt, *args, **kwargs))