feat: allow fixing the vertical order of Sankey nodes

[adamreeve]

Fixes #4373

Follow up to #7830

This exposes the nodeSort method added to d3-sankey, to allow disabling the default ordering algorithm and enforcing that the vertical order should match the order of nodes in the input data.

Note that the nodeSort method in d3-sankey can be a method that compared two nodes (see the docs), but for many users I think just providing a way to pass null instead of the default undefined is sufficient. But maybe this could be future-proofed somehow to support using a comparison method in future? Although I'm not sure how feasible it is to make that work in plotly.

The nodeSort option is not supported by d3-sankey-circular, so is not used for circular Sankey diagrams (see #7689 (comment) for more context).

[camdecoster]

This seems great. I've requested a few small changes. What do you think of adding support for link sort?

[camdecoster]

Suggested change

	var input_sort = trace.node.sort === 'input';
	const inputNodeSort = trace.node.sort === 'input';

[camdecoster]

Suggested change

	if(circular && input_sort) {
	Lib.error('Circular Sankey diagrams do not support the "input" node.sort mode; falling back to the default sort.');
	}

[camdecoster]

Suggested change

	}
	if (inputNodeSort) {
	if (circular) {
	Lib.warn('Circular Sankey diagrams do not support the "input" node.sort mode; falling back to the default sort.');
	} else {
	// Passing null keeps nodes in their input order
	sankey.nodeSort(null);
	}
	}

[camdecoster]

Suggested change

	'If the value is `auto` (the default), the vertical order of nodes will be determined automatically',
	'by the layout.',
	'If the value is `input`, the vertical order is kept the same as the order in the input node array'
	'For `auto` (the default), the vertical order of nodes will be determined automatically by the layout.',
	'For `input`, the vertical order of nodes is kept the same as the order in the input array.'

[camdecoster]

I think this mock can be deleted since all of the other sankey mocks use the auto sort.

[camdecoster]

Suggested change

	"title": { "text": "Sankey with fixed vertical node ordering" },
	"title": { "text": "Sankey with vertical node ordering matching the input array" },

[camdecoster]

Suggested change

	var errors = [];
	spyOn(Lib, 'error').and.callFake(function (msg) {
	errors.push(msg);
	});
	var warnings = [];
	spyOn(Lib, 'warn').and.callFake(function (msg) {
	warnings.push(msg);
	});

[camdecoster]

Suggested change

	expect(errors.length).toBe(1);
	expect(warnings.length).toBe(1);