New River Area Chart Type

[Yuqing Liu]

Is your feature request related to a problem? Please describe.
Currently, ngx-charts does not support a river chart similar to https://echarts.apache.org/examples/en/editor.html?c=themeRiver-basic. It can visualizes data in a way that resembles the flow of a river and highlight patterns and trends.

Describe the solution you'd like
A new chart type that is similar to stacked area chart but is symmetrical horizontally. It emphasizes the changes in data as it progresses across different x values, allowing viewers to easily identify trends, patterns, and shifts in the data over time or other variables.

Describe alternatives you've considered
n/a
Additional context
n/a