Add support for dataframes that have toPandas method

[LiamConnors]

Add support for dataframes that have toPandas method

Code PR

• I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the codegen files and not generated files.
• I have added tests (if submitting a new feature or correcting a bug) or
  modified existing tests.
• For a new feature, I have added documentation examples in an existing or
  new tutorial notebook (please see the doc checklist as well).
• I have added a CHANGELOG entry if fixing/changing/adding anything substantial.
• For a new feature or a change in behaviour, I have updated the relevant docstrings in the code to describe the feature or behaviour (please see the doc checklist as well).

[alexcjohnson]

💃 Nice and easy 😎

[nicolaskruchten]

FWIW, vaex uses .to_pandas_df() rather than .to_pandas() or .toPandas() :P

[alexcjohnson]

might_be_a_converter = [
    method for method in dir(df_not_pandas)
    if 'to' in method.lower()
    and 'pandas' in method.lower()
    and method.lower().index('to') < method.lower().index('pandas')
]
if might_be_a_converter:
    args["data_frame"] = getattr(df_not_pandas, might_be_a_converter[0])()

🙃 probably not, but we could add to_pandas_df explicitly as well.

[alexcjohnson]

Not a big deal, but it would be a bit cleaner to invert this:

if hasattr(df_not_pandas, "toPandas"):
    args["data_frame"] = df_not_pandas.toPandas()
elif hasattr(df_not_pandas, "to_pandas_df"):
    args["data_frame"] = df_not_pandas.to_pandas_df()
elif hasattr(df_not_pandas, "to_pandas"):
    args["data_frame"] = df_not_pandas.to_pandas()
else:
    raise exc