Bump bevy to 0.7

[linkmauve]

I tried to make a single commit per change, so that people looking at the history will understand the changes better even if they aren’t familiar with bevy.

This is currently draft because I need help with updating the shaders plugin, the internals got reworked and we can’t really use the same method as before, so help welcome.

The blog post will also need updating once this PR is merged, so that people following it don’t get confused.