Delegation works with reserved words passed to `:to`

Fixes #16956.
 Updated comment about features of fixtures

 - Added a note about some features which are not dependent on
   auto-generated ID's.
 - [ci skip]
[ci skip] ActionRecord CHANGELOG docs fixes
Merge pull request #16964 from Agis-/issue-16956

Make delegation work with the reserved words passed to `:to`
Merge pull request #16975 from lethalbrains/master

[ci skip] ActionRecord CHANGELOG docs fixes
Merge pull request #16973 from prathamesh-sonpatki/fixtures-features

 Updated comment about features of fixtures