…lumns (juanmiguelbesada)

This PR was squashed before being merged into the 3.4 branch.

Discussion
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[DoctrineBridge]  indexBy could reference to association columns

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tickets       | Fix #37982 <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT
| Doc PR        | -
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This is my approach to solve #37982. It partials reverts @xabbuh PR #38604

This is my first Symfony contribution, so please, tell me if I need to do something more or something is wrong.

Also, this bug affects 4.x and 5.x versions. I think merging in this branches is done automatically. If not, please tell me.

Thanks you

Commits
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f9a0e00 failing test for issue 38861
4c36145 [DoctrineBridge]  indexBy could reference to association columns