[data grid] New api method: getRowGroupChildren

[flaviendelangle]

Closes #4270
Part of #4248

Doc preview:https://deploy-preview-4304--material-ui-x.netlify.app/x/react-data-grid/row-grouping/#get-the-rows-in-a-group

Add a new method apiRef.current.getRowGroupChildren

By default, this method returns all the rows inside a grouping criteria except the auto generated ones (do not return the subgroups but there descendants).

For instance the rows of Group A are [Element 1, Element 2, Element 3], the rows of Group A A are [Element 1, Element 2]

Group A
  Group A A
    Element 1
    Element 2
    Aggregation Footer
  Group A B
    Element 3

• Support filtering
• Support sorting
• Support models with several elements
• New method getGroupRowIdFromPath to easily create the id of a grouping row. If you prefer we can do the opposite (provide the path to getGroupingCriteriaRows and add a method getGroupPathFromGroupRowId)
• Doc example
• Tests

[mui-bot]

These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	243.9	493.9	435.6	372.74	105.369
Sort 100k rows	ms	417.5	997.7	782.5	720.06	195.302
Select 100k rows	ms	124.8	225.8	174.8	176.78	38.895
Deselect 100k rows	ms	104.8	273.6	151.1	172.88	59.999

Generated by 🚫 dangerJS against 25fb4d7

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[joserodolfofreitas]

I think the getGroupingCriteriaRow name might be a bit confusing.
If I understand it correctly, it returns the grouped rows using the data grid's visualization criteria, and if that's the case, I'd be in favor of simplifying the name to getGroupedRows.

GroupId, applyFiltering and applySorting as parameters help complement the function description.

It'd also be more coherent when actually trying to get rows by GroupingCriteria when combing the call with getGroupRowIdFromPath, which I'd then propose to rename to getGroupIdForGroupingCriteria

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[joserodolfofreitas]

https://deploy-preview-4304--material-ui-x.netlify.app/x/react-data-grid/group-pivot/#get-the-rows-in-a-group

Where's the page section under the new structure?
I thought I'd find it here https://deploy-preview-4304--material-ui-x.netlify.app/x/react-data-grid/row-grouping/

[flaviendelangle]

@joserodolfofreitas oops I lost it when merging with the new split doc page.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[flaviendelangle]

I am merging it since it has been approved with its prior name