fix(axis):null value item on category axis should be able to show tooltip

[Justin-ZS]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

If the chart uses dataset/axis.encode, the null value items on category axis cannot trigger axis tooltip.(NG)
Try demo

echarts/src/scale/Ordinal.ts

Lines 143 to 147 in b5c4a66

	contain(rank: OrdinalRawValue | OrdinalNumber): boolean {
	rank = this.parse(rank);
	return scaleHelper.contain(rank, this._extent)
	&& this._ordinalMeta.categories[rank] != null;
	}

This check will ignore null value items on category axis, although null is a valid value.

But if the chart uses axis.data, the null value items on category axis can trigger axis tooltip.
In this case, the axis.data will be parsed by getName -- null becomes "null".

echarts/src/data/OrdinalMeta.ts

Lines 50 to 61 in b5c4a66

	static createByAxisModel(axisModel: Model): OrdinalMeta {
	const option = axisModel.option;
	const data = option.data;
	const categories = data && map(data, getName);
	return new OrdinalMeta({
	categories: categories,
	needCollect: !categories,
	// deduplication is default in axis.
	deduplication: option.dedplication !== false
	});
	};

Fixed issues

#20774

Details

Before: What was the problem?

After: How does it behave after the fixing?

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

N.A.

Others

Merging options

• Please squash the commits into a single one when merging.

Other information

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