Propagate transforms in fixed update

[james7132]

Objective

Fix #7836. GlobalTransform is not updated in FixedUpdate.

Solution

Add it to FixedUpdate, keep the same system sets, clean up the code a bit.

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Changelog

Changed: Transform propagation now runs in CoreSet::FixedUpdate.

[irate-devil]

We will need to add base sets to the FixedUpdate schedule, otherwise users will need to explicitly run their systems before transform propagation.

[james7132]

Marking this as blocked on #7835 then.

[hymm]

won't this potentially run propagate_transforms multiple times in a frame even if a user isn't using fixed update? Or is the cost of that negligible with the change checking?