feat: add new stacking strategies

[villebro]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

This PR adds a new property stackStrategy to the SeriesStackOptionMixin which defaults to samesign (current behavior). Associated PR on the docs repo: apache/echarts-doc#255

Fixed issues

• Closes Stacked line chart with negative values #9317
• Close Negative line calculate stack  #9141
• Close 折线图，area面积区域填充色的时候，origin配置start的时候，是否可以从折线的开启面积区域的折线图最小值开始填充 #13747
• Close After setting the minimum value of Y-axis min, the data is stacked and the plot is missing #15083
• Close Stack area not working properly below zero on Y axis. #14365

Details

Before: What was the problem?

Currently stacking is only applied if the cumulative sum has the same sign as the value to be stacked. This makes it impossible to mix positive and negative values in the same series, something typically needed when creating confidence bands:

After: How is it fixed in this PR?

Here we introduce the following new stacking options:

• all: stack all values, irrespective of the sign of the stackable value:

• positive: only stack positive values:

• negative: only stack negative values:

We also add the strategy samesign which corresponds to the current behavior which we default to to avoid introducing a breaking change. However, I propose defaulting to all in the next major version, as I assume this is the behavior users will expect to see.

Misc

• The API has been changed (apache/echarts-doc#xxx).
• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

New test cases added to the area-stack.html test.

Others

Merging options

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

Other information

[echarts-bot]

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[villebro]

Docs for the proposed feature: apache/echarts-doc#255

[villebro]

@pissang let me know if you feel this should be implemented some other way so I can change the PR accordingly

[pissang]

@villebro Thanks for the wonderful work! All looks good to me except a tiny code style issue.

[susiwen8]

This could fix a lot of issues. I have added in PR description

[echarts-bot]

Congratulations! Your PR has been merged. Thanks for your contribution! 👍