[10.x] Fix cursor paginate with union and column alias

[thijsvdanker]

When using cursorPaginate on a query with a union the where clause on the union uses the wrong column name.

Table Post:

id
start_time

Table News:

id
created_at

Post::toBase()
    ->select('id', 'start_time as created_at')
    ->union(News::toBase()->select('id', 'created_at'))
    ->orderBy('created_at')
    ->cursorPaginate(10, ['created_at']);

Should sort Post by the start_time column and News by the created_at column.

The current implementation sorts both Post and News by the start_time column.

This is similar to #50809 but with a dedicated test to confirm the issue.

[thijsvdanker]

Is there anything I can do to move this forward?

[driesvints]

@thijsvdanker not really. Just await a review by @taylorotwell.

[crynobone]

@thijsvdanker Do we still need this if #50884 PR get merged?

[thijsvdanker]

@crynobone Yes we do.

I've just ran the tests in this PR against the code in #50884 and they still fail for the same reason.

[crynobone]

@thijsvdanker I feel like we should prioritize integration tests for this instead of just mocking everything.

[thijsvdanker]

@crynobone I agree.
I have a busy week but I'll see if I can make an integration test later this week.

[thijsvdanker]

@crynobone I've added an integration test.

[taylorotwell]

@thijsvdanker would you remind resolving the conflicts? Does the integration test you added fail without your code changes?

[thijsvdanker]

@taylorotwell I've resolved the conflicts.
This PR shows both the integration test and the mocked test fails without my changes: #51088