[Feature] get bar gap in renderItem,

[littlegolden]

What problem does this feature solve?

to implement this style, use renderItem to get points for each stacked series, the point from api.coord([xValue, yIndex]) is the center of the bar item, to move it to the bottom of the bar item, division the barLayout[i].bandWidth by 2 and minus with y point value, but result is not at the bottom of bar item, but the center of the gap, seems that the bandWidth contains the gap, how to minus the gap height?

see example

example