Add APIs for refreshing individial items in collections

[Jacalz]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

This was discussed on the call yesterday. There are a few cases where you know which item index needs a refresh but the only way to refresh it is to refresh the whole collection using .Refresh(). We should add an API to refresh individual items in collections (cells in Table, rows in List and so on). As a bonus, the collection widget can be smart and avoid a refresh if the item is not currently visible.

Is it possible to construct a solution with the existing API?

It should be possible

Describe the solution you'd like to see.

Add an API to refresh individual items in collections (cells in Table, rows in List and so on).

[andydotxyz]

This is completed for v2.4.0 :)