Add label to transform propagation system

[aevyrie]

Adds a label to the GlobalTransform transform propagation system. This is needed due to recent changes in the scheduler. I've been experiencing issues with systems running prior to GlobalTransforms being updated. A label is needed on the propagation system to allow me to specify a system dependency.

[TheRawMeatball]

Hmm, there is a lot of other labels that need to be added as we resolve all internal ambiguities, so it might not be a good idea to add these labels one-by-one.

[aevyrie]

Hmm, there is a lot of other labels that need to be added as we resolve all internal ambiguities, so it might not be a good idea to add these labels one-by-one.

Right, but most of these are for internal disambiguation, correct? This is a label that really needs to be exposed publicly, so we can specify it as a system dep. The other reason I thought it was worth submitting as a lone label is because there might be larger discussion around this. Bugs caused by GlobalTransform system ordering are really common in my experience.

Edit: e.g. #1439

[alice-i-cecile]

I think we should merge #1456 in preference to this due to it being a bit more complete.

[aevyrie]

I'll close this then. Thanks for the heads up @alice-i-cecile!