Raise a clear error for unsupported marginal plot types

[eugen-goebel]

Link to issue

Closes #4654

Description of change

make_trace_spec now raises a clear ValueError listing the supported marginal plot types when an unsupported value is passed to marginal_x, marginal_y or marginal, instead of failing later with a cryptic 'NoneType' object has no attribute 'constructor'.

Demo

Before:

>>> import plotly.express as px
>>> px.scatter(x=[1, 2, 3], y=[2, 3, 4], marginal_x="density")
AttributeError: 'NoneType' object has no attribute 'constructor'

After:

>>> import plotly.express as px
>>> px.scatter(x=[1, 2, 3], y=[2, 3, 4], marginal_x="density")
ValueError: Invalid value 'density' for `marginal_x`. Supported marginal plot types are: 'rug', 'box', 'violin', 'histogram'.

Testing strategy

Adds test_unsupported_marginal_raises_clear_error in tests/test_optional/test_px/test_marginals.py, which asserts that an unsupported value for marginal_x, marginal_y and the singular marginal argument raises a ValueError. The existing marginal tests still pass.

Additional information (optional)

The singular marginal argument is normalised to marginal_x / marginal_y before make_trace_spec runs, so a single check covers all three parameters.

Guidelines

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