Make glow Send + Sync again

[surban]

• Reverts Change Arc<glow::Context> to Rc<glow::Context> #3598
• Closes Revert "Change Arc<glow::Context> to Rc<glow::Context>" #3598 #3645

[emilk]

Nice one! Unfortunately this is a breaking change, so will have to wait for the 0.25 release

[marshray]

I'm working on my first egui project using glow and three-d.
It's just at the 'triangle' stage right now, but you can see it here.

Thanks for the great starting template @emilk! And for the fix @surban!

I have it working with patches, but it would be just super great if the three projects would release versions that work together.

Thanks,

• Marsh

This is how I'm currently working around this:

• https://github.com/marshray/sunangle/blob/bbdd5f6f1c5c1f3a9929d8cf332f96fd77f852bd/Cargo.toml#L11C1-L73C100
• https://github.com/marshray/surban.egui/blob/baf6e8ba316b8e5edff9fbeab2a9a5134856a21c/Cargo.toml#L49C1-L62C1
• https://github.com/marshray/three-d/blob/0cd8b4cc2d5fc52a5e5ae3dfe1458c4b1056d653/Cargo.toml#L19C1-L60C1

ref: asny/three-d#421
ref: grovesNL/glow#268