refactor(funnel): 支持尖底漏斗图以及样式设置

[visiky]

PR includes

• feat: 增加 shape 配置，支持尖底漏斗图(金字塔). fixed [Feature Request] 希望"漏斗图"增加"尖底漏斗图" #2305
• feat: 增加 funnelStyle 配置，支持配置漏斗图样式
• add / modify test cases
• documents, demos

Screenshot

Before	After
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[github-actions]

🎊 PR Preview 9266947 has been successfully built and deployed to https://antvis-G2Plot-preview-pr-2634.surge.sh?type=diff&date=2021-06-13

🕐 Build time: 84.715s

_{🤖 By surge-preview}

[coveralls]

Pull Request Test Coverage Report for Build 932542867

• 24 of 24 (100.0%) changed or added relevant lines in 6 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.003%) to 96.053%

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Files with Coverage Reduction	New Missed Lines	%
src/plots/funnel/adaptor.ts	1	98.48%

Totals
Change from base Build 930578592:	-0.003%
Covered Lines:	5991
Relevant Lines:	6085

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💛 - Coveralls