feat(legend): 图例支持回调设置 marker

[visiky]

ref: antvis/component#228, antvis/G2Plot#2558

Checklist

• npm test passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Description of change

[github-actions]

🎊 PR Preview 5b13bb5 has been successfully built and deployed to https://antvis-G2-preview-pr-3448.surge.sh?type=diff

🕐 Build time: 84.649s

_{🤖 By surge-preview}

[coveralls]

Pull Request Test Coverage Report for Build 887416478

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.008%) to 93.445%

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Files with Coverage Reduction	New Missed Lines	%
src/util/legend.ts	1	96.77%

Totals
Change from base Build 877264083:	-0.008%
Covered Lines:	11045
Relevant Lines:	11460

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💛 - Coveralls