Save the figure to a file.

def save_figure_as(self, fig, fmt):
        """Save the figure to a file."""
        fext, ffilt = {
            'image/png': ('.png', 'PNG (*.png)'),
            'image/jpeg': ('.jpg', 'JPEG (*.jpg;*.jpeg;*.jpe;*.jfif)'),
            'image/svg+xml': ('.svg', 'SVG (*.svg);;PNG (*.png)')}[fmt]

        figname = get_unique_figname(getcwd_or_home(), 'Figure', fext)

        self.redirect_stdio.emit(False)
        fname, fext = getsavefilename(
            parent=self.parent(), caption='Save Figure',
            basedir=figname, filters=ffilt,
            selectedfilter='', options=None)
        self.redirect_stdio.emit(True)

        if fname:
            save_figure_tofile(fig, fmt, fname)