[RFR] Fix handling of deleted references

[djhi]

Problem

When a <ReferenceManyField> displays a <DataGrid> with a DeleteButton on each row, optimistically deleting a reference will set its row into loading state but won't actually remove it until the action is resolved.

Solution

Handle the DELETE effects in the oneToMany reducer by checking whether we have references related to the deleted item resource and removing the deleted item from them.

[ThieryMichel]

Ain't the total equal to the number of ids ?
If so, you could filter to get the kept id, and returns

{
    ids: keptIds,
    total: keptIds.length
}

If not the test should reflect that fact.

[ThieryMichel]

Also refactor removeDeletedReference to use removeDeletedReferences.

[fzaninotto]

instead of filtering twice just to count the number of elements to filter out, why don't you just count once and then compare the length to the length of the original key?

    const idsToKeep = previousState[key].ids.filter(
        id => !removedIds.includes(id)
    );
    if (idsToKeep.length === previousState[key].ids.length) {
        return previousState;
    }
    return {
        ...previousState,
        [key]: {
            ids: idsToKeep,
            total: idsToKeep.length,
        },
    };