Generate warnings when incorrectly accessing Transform or GlobalTransform

[aevyrie]

What problem does this solve or what need does it fill?

Updating Transform late or reading GlobalTransform early are very common issues that result in a number of help requests and bugs in general.

What solution would you like?

Generate a warning in debug mode any time a Transform is ever mutated after GlobalTransform is propagated or a GlobalTransform is accessed before it has been updated that frame.

What alternative(s) have you considered?

1. Do nothing, accept this as a source of error.
2. Develop some general method of specifying component dependencies.
3. Keep positions from the last frame in GlobalTransform and propagate Transforms at the end of the frame to ensure that worst case, systems accessing it will be a frame out of date, but still work. This could be accompanied with an error message.

[MinerSebas]

Something else to consider is that most User Code should only read from GlobalTransform, as its Values are managed and overrriden by Bevy itself.

[mockersf]

Generate a warning in debug mode

With the general recommendation being "run in release", I wonder if it wouldn't be better to add a "debug" feature enabled by default (probably with a better name though... "training-wheels"? "clippy"?)
I think disabling default features to pick only the ones you want when you release a game is the good thing to do (anyway it's what I do)

[Ratysz]

Something else to consider is that most User Code should only read from GlobalTransform, as its Values are managed and overrriden by Bevy itself.

#1460 should take care of that.

[alice-i-cecile]

For reference, this should be improved by #68.

[nicopap]

GlobalTransform doesn't have a Transform field anymore, and since, #7134 it's not even possible to mutate it.

The 1-frame lag issue is still an open question, but it seems very difficult to design a system to catch it and warn users about it.