[Feature] Conversion rate of adjacent two layers in funnel chart漏斗图相邻两层的转化率

### What problem does this feature solve?

Current situation rate=current_layer_num/sum(every_layer_num)
lay1: A, 100 rate=100/(100+80+50)=0.4347
lay2:B, 80 rate= 80/(100+80+50)
lay3:C,50 rate=50/(100+80+50)

expected result: rate = current_layer_num/last_layer_num
lay1: A, 100(top_lay_num)
lay2:B, 80 rate= 80/100=0.8
lay3:C,50 rate=50/80=0.625 (here is the main difference)

### What does the proposed API look like?

Current situation rate=current_layer_num/top_layer_num
lay1: A, 100(top_lay_num)
lay2:B, 80 rate= 80/100=0.8
lay3:C,50 rate=50/100=0.5

expected result: rate = current_layer_num/last_layer_num
lay1: A, 100(top_lay_num)
lay2:B, 80 rate= 80/100=0.8
lay3:C,50 rate=50/80=0.625 (here is the main difference)

How can we achieve the expected result?