Nested element DX improvements

[brandonkelly]

Description

Adds NestedElementQueryTrait, which can be added to element query classes to provide fieldId, ownerId, primaryOwnerId, allowOwnerDrafts, and allowOwnerRevisions params.

class MyElementQuery extends ElementQuery
{
    use NestedElementQueryTrait;

    protected function beforePrepare(): bool
    {
        // ...

        $this->applyNestedElementParams('elementable.fieldId', 'elementtable.primaryOwnerId');
    }
}

Also adds NestedElementTrait::saveOwnership(), which can be called from elements’ afterSave() methods to save their ownership data in the elements_owners table.

class MyElement extends Element
{
    public function afterSave(bool $isNew): void
    {
        // ...

        $this->saveOwnership($isNew, '{{%elementtable}}');
    }
}

Related issues

• Abstract `owner` condition for use alongside NestedElementManager #15882