FIX Include default_sort in sortChildren method

[emteknetnz]

Issue silverstripe/gha-ci#37

Fix https://github.com/silverstripe/silverstripe-asset-admin/runs/7492970779?check_suite_focus=true#step:12:213
Then I should see the gallery item "xsubfolder1" in position "1"#

Not sure why this wasn't showing up on the travis graphql 4 behat jobs, as I was able to replicate this locally using both php 8.1 with mysql 8 as well as php 7.4 with mysql 5.7. I replicated by creating a pair of folders 'xsubfolder1' and 'zsubfolder2' then renaming them to 'zsubfolder1' and 'xsubfolder2' respectively. They should have then sorted by 'xsubfolder2', 'zsubfolder1' but they did not

This issue was not replicatable using graphql3, so this PR matches the graphql3 behaviour.

[GuySartorelli]

this PR matches the graphql3 behaviour

Just to clarify, did you take any code from the legacy/graphql directory for this, or did you look at the way this behaves with GraphQL3 and replicate that behaviour with new code?

[emteknetnz]

I looked at the GraphQL 3 behavior and copied that

[GuySartorelli]

There are some considerations in the GraphQL3 implementation that are not taken into account here, such as custom aggregate sort fields:

silverstripe-asset-admin/_legacy/GraphQL/FolderTypeCreator.php

Lines 185 to 188 in 17163c8

	// some fields may be surrogates added by extending augmentSQL
	// we have to preserve those expressions rather than auto-generated names
	// that SQLSelect::addOrderBy leaves for them (e.g. _SortColumn0)
	$field = $query->expressionForField(trim($field, '"')) ?: $field;

It might be worth considering using the existing GraphQL3 logic which preserves all existing sort orders (including default sort which is applied in DataObject::get()).

The sortChildren() method has ?Sortable as its type for $list but I think it would be safe to bump this to ?DataList since we know this admin section only handles DataList anyway - alternatively, you could do a if ($list instanceof DataList) check and do it the gql3 way if true, and this new way if false.

silverstripe-asset-admin/_legacy/GraphQL/FolderTypeCreator.php

Lines 180 to 209 in 17163c8

	$list = $list->alterDataQuery(static function (DataQuery $dataQuery) {
	$query = $dataQuery->query();
	$existingOrderBys = [];
	foreach ($query->getOrderBy() as $field => $direction) {
	if (strpos($field, '.') === false) {
	// some fields may be surrogates added by extending augmentSQL
	// we have to preserve those expressions rather than auto-generated names
	// that SQLSelect::addOrderBy leaves for them (e.g. _SortColumn0)
	$field = $query->expressionForField(trim($field, '"')) ?: $field;
	}
	$existingOrderBys[$field] = $direction;
	}
	// Folders should always go first
	$dataQuery->sort(
	sprintf(
	'(CASE WHEN "ClassName"=%s THEN 1 ELSE 0 END)',
	DB::get_conn()->quoteString(Folder::class)
	),
	'DESC',
	true
	);
	foreach ($existingOrderBys as $field => $dir) {
	$dataQuery->sort($field, $dir, false);
	}
	return $dataQuery;
	});

[GuySartorelli]

Looks good, merge on green