make the `._has_subplots` method from `go.Figure` accessible

In some cases, when writings callbacks that only update a subplot of a Figure, it is useful to know if the figure will accept an append_trace to a specific location, or if add_trace should be used instead.

I use this workaround (using a try/except isn't great):

    if fig._has_subplots():
        fig.append_trace(trace, 1, 1)
    else:
        _ = fig.add_trace(trace)

If I only use fig.append_trace(trace, 1, 1), I get Exception: In order to reference traces by row and column, you must first use plotly.tools.make_subplots to create the figure with a subplot grid.

If I only use fig.add_trace(trace), the layout gets messed up.

Could it be possible to make this method public?

Inspecione a implementação de _has_subplots de go.Figure e a API pública Figure em torno de append_trace, add_trace e make_subplots. O trabalho estará concluído quando os chamadores puderem usar uma verificação pública para determinar se as referências de trace de linha e coluna são válidas sem depender de uma solução alternativa com try/except, preservando o comportamento existente dos subplots.