Update to Bevy 0.12

[vav-dev]

No description provided.

[thisjaiden]

I looked into making a quick and dirty PR to migrate but found that bevy/#10377 is blocking on updating the embedded shaders to the new system. There are a few workarounds, but none are perfect. Happy to help if anything gets sorted, though I'm not exactly sure what that means 😅

Obviously no one wants to wait for Bevy 0.12.1 but I'm not sure what the alternative in the meantime is. I tried the embedded_asset(app, "src/", "..."); trick (only currently known workaround to #10377) but found it didn't work in my environment. We could embed it ourselves, though I lean away from adding cruft and bandaids.

If nothing happens in a day or two I'll try to clean up my PR and post what is done, though it's not enough to get stuff running. Advice from @Toqozz requested!

[pietrosophya]

This should do it.