Generic propagation should happen in `PostUpdate`

[alice-i-cecile]

DreamerTalin: Propagation happens in Update schedule, which can cause a 1-frame delay unless you ensure that your mutations of the propagation source happen earlier in the schedule.

Cart: I think propagation should happen in PostUpdate for this reason

[alice-i-cecile]

Remember to update the docs for the plugin too!

[cart]

More context: #20354 (comment)

[alice-i-cecile]

@cart in #20433 (comment):

I think the default value is kind of hard to pick. With Update, it means you don't need to think about PostUpdate ordering (easier on the propagated component dev). With PostUpdate, you always run after all game logic (easier on the propagated component consumers), but the author needs to be very careful about PostUpdate ordering.

I'm cool with leaving this in Update for now, but I think Propagate should be done in PostUpdate.

[ickshonpe]

Resolved by #20433 removing the default instead.

[alice-i-cecile]

Reopening for just a bit: we still need to move the propagation for textfont.