feat: Chord charts

[Ovilia]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fixed issues

Details

The following are some highlights of the Chord implemented by this Pull Request.

Edges With Gradient

Other values include 'target' (using target color as edge color) and 'source' (using source color as edge color).

focus.emphasis Behaves Similar To Sankey

This is effect of focus: 'adjacency', which I use as the default value since it looks well and the interaction is more intuitive. Other values include 'none'and'self'`.

minAngle and padAngle

The current implementation of minAngle and padAngle have bugs with Pie Series (#20603) and Sunburst (#20602), so I re-implemented the logic in Chord Series. The bugs can be fixed with Pie and Sunburst in the future with the similar implementation of Chord.

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

[echarts-bot]

Thanks for your contribution!
The community will review it ASAP. In the meanwhile, please checkout the coding standard and Wiki about How to make a pull request.

The pull request is marked to be PR: author is committer because you are a committer of this project.

⚠️ MISSING DOCUMENT INFO: Please make sure one of the document options are checked in this PR's description. Search "Document Info" in the description of this PR. This should be done either by the author or the reviewers of the PR.

[github-actions]

The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-20522@bfed24a

[echarts-bot]

Document changes are required in this PR. Please also make a PR to apache/echarts-doc for document changes and update the issue id in the PR description. When the doc PR is merged, the maintainers will remove the PR: awaiting doc label.