Add event listeners on month/date change by navigator at Calendar

[Parapheen]

This function solves the problem (这个功能解决的问题)

I've come across a use case to load data with query for each month. Thus, displaying events happening this month. Would be great to watch for month, year when user navigates Calendar, uploading necessary info for target month and year.

Expected API (期望的 API)

basically add event same as update:value. Unfortunately, I can't go deeper in implementation due to lack of understanding xd