Update to glam 0.21.2

[alice-i-cecile]

As @dependabot tried in #5112, this migration should be relatively simple. However, we need to migrate off the deprecated const_vec macros and use the much nicer Vec3::from_array methods instead.

This should be nice and simple, but is too hard for a little robot.

[james7132]

I think hexasphere needs to be updated too

[bitshifter]

I think it's failing due to the encase dependency which will need to be updated first - https://github.com/bevyengine/bevy/runs/7067058036?check_suite_focus=true.

Also Vec3::new and Vec3::splat are const fn as well so there are a few options for moving off the macros.