Update to bevy v0.4.0

[Fedcomp]

Tests pass (my linux), it compiles (my linux). Not sure if this PR is usefull for anyone.

Big thanks to @alec-deason ( #30 ) it was really usefull reference while i was updating bevy_rapier and i saved a lot of my time thanks to it.

• Fix debug_ui timer Regression: bevy 0.4: Text value update is not rendered when on stage::POST_UPDATE bevyengine/bevy#1102. Right now it is never updated if text update system is on stages::POST_UPDATE stage. Works if on stages::UPDATE.
• Fix sizes of boxes in boxes3, right now it's mesh is about 2x smaller than it's colliding box.
• Ensure all other examples are working same as in bevy 0.3.0

[sebcrozet]

Hi! Thank you for this PR. How does this differ from #30 exactly?

[Fedcomp]

@sebcrozet mine targets stable bevy 0.4.0 (unlike the #30 ) and i am in the process of fixing examples (which is also not fixed in that PR).
For example boxes3 example has 2x smaller boxes than their invisible colliding boxes and physics simulation speed text is simply not updating from default text (something with font rendering changes i guess, it works if i move text update system to update stage).

I am going to make this completely ready to be merged with all examples working and all issues fixed (even if i have to open issues in the bevy itself).

I see no problem if you update bevy_rapier on your own. I had to update it to get new version faster for my own game, and decided to share my work and make it completely mergeable with zero issues.

[Fedcomp]

apparently size of Mesh::from(shape::Cube { size: 1.0 }) is 2x smaller now.

[Fedcomp]

And POST_UPDATE for debug ui text is no longer an option: bevyengine/bevy#1102 (comment)

[Fedcomp]

Mesh::from(shape::Cube { size: 2.0 }) go brrr

[Fedcomp]

I've moved bevy ui diagnostics plugin to UPDATE stage instead of POST_UPDATE due to issue with perfomant fonts in bevy 0.4.0.

[Fedcomp]

Examples visually looks the same as in bevy_rapier for bevy 0.3.0 (i did side by side comparison). But simulation feels like x2 faster.
@sebcrozet it would be cool to get PR review from you, it's probably ready to be merged.

[sebcrozet]

Seems all good. Thanks!

[sebcrozet]

And thanks to @alec-deason for their initial work on this with #30!

[sebcrozet]

I made a release of bevy_rapier 0.7 which includes these changes.