Backport prevent deadlocks with load interlock and DB lock to 5-1-stable

[BrentWheeldon]

Summary

This backports #31035 which fixes an issue where competing threads deadlock each other to the 5.1 branch.

• Thread A holds the load interlock but is blocked on getting the DB lock
• Thread B holds the DB lock but is blocked on getting the load interlock (for example when there is a Model.transaction block that needs to autoload)

This solution allows for dependency loading in other threads while a thread is waiting to acquire the DB lock.

[rails-bot]

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[rails-bot]

Warning

• Pull requests are usually filed against the master branch for this repo, but this one is against 5-1-stable. Please double check that you specified the right target!

[BrentWheeldon]

Thanks, @rafaelfranca!