[8.x] Fix Self-Relation issue in withAggregate method

[khalilst]

This PR is created in following of the PR #35389 .

It modifies the getRelationCountHash to provide a way to predict the hash.
It prevents increasing $selfJoinCount, if called like this:

$relation->getRelationCountHash(true)

[taylorotwell]

What does $fixed mean? Can that be given an actually descriptive variable name?

[khalilst]

@taylorotwell OK. I'm gonna change the $fixed into $lockCount.

[bjuppa]

@khalilst perhaps you can just copy the failing test from #35389 into this PR?

[taylorotwell]

No tests?

[taylorotwell]

Added test.

[khalilst]

@bjuppa as I have commented in your PR, I was waiting for permission to use your test.
Btw, it was added by @taylorotwell .
Thank you all.

[dbakan]

Could this be a breaking change? Changing the signature of getRelationCountHash? I‘m not sure, just asking.

[khalilst]

@dbakan No. It's not. Because of the default value of $lockCount = false the previous signature supported.
Also, the instance of the $relation have been checked in withAggregate for special case.

[GrahamCampbell]

The breaking change would be for people extending the class and overriding the method.

[dbakan]

@GrahamCampbell That's what I thought.

Another idea might have been to add a new method getCurrentRelationCountHash.

[dbakan]

@khalilst Just to clarify what I meant: https://3v4l.org/KIleN
But maybe this not a bigger problem. Nice work anyway, thanks!