FIX Add eagerloaded data to ALL relevant lists

[GuySartorelli]

Description

When a record belongs to multiple many_many (and maybe has_many) relations and you eagerload it and chained relations from it, you can end up in a scenario where the eagerloaded data doesn't get added to some of the relation lists it belongs to. More details in the linked issue.

Manual testing steps

1. Add a breakpoint on DataList::getFinalisedQuery()
2. Run this code

   use SilverStripe\Security\Member;
   $list = Member::get()->eagerLoad('Groups.Permissions');
   foreach ($list as $member) {
       foreach ($member->DirectGroups() as $group) {
           foreach ($group->Permissions() as $perm) {
               echo '';
           }
       }
   }

3. Check the trace each time the breakpoint is hit. It should only be hit once directly from the above code.

You could also add a breakpoint in the above code itself, and check that each list being looped over (with exception for the top loop) is an instance of EagerLoadedList, not DataList.

Issues

• https://github.com/silverstripe/silverstripe-framework/issues/11138

Pull request checklist

• [x] The target branch is correct
  • See picking the right version
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  • Small amounts of additional linting are usually okay, but if it makes it hard to concentrate on the relevant changes, ask for the unrelated changes to be reverted, and submitted as a separate PR.
• [x] The commit messages follow our commit message guidelines
• [x] The PR follows our contribution guidelines
• [x] Code changes follow our coding conventions
• [x] This change is covered with tests (or tests aren't necessary for this change)
• [x] Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• [x] CI is green

[GuySartorelli]

Note that I have confirmed the new test fails without this fix.

[GuySartorelli]

Oops! Good catch. Targetted to 5.1