Use static_assertions to check for trait impls

[BD103]

Objective

• Tests are manually checking whether derived types implement certain traits. (Specifically in `bevy_reflect.)
• Add static assertions to bevy_utils for compile-time checks #11182 introduces static_assertions to automatically check this.
• Simplifies Reflect test in Implement TypePath for EntityHash #11195.
• Closes Use static_assertions crate for asserting that types impl Reflect #11196.

Solution

• Add static_assertions and replace current tests.

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I wasn't sure whether to remove the existing test or not. What do you think?

[alice-i-cecile]

Looks good! Let's keep the other tests for now: these seem useful enough. We could split them out further, but I won't block on it.

[BD103]

Awesome! I'll remove the TODO comments.

I'm going to check if any other crates use the same should_impl test style, and I'll fix CI too.

[alice-i-cecile]

@cBournhonesque, have time for a quick review?

[BD103]

I couldn't find any other tests that would work for this. As long as CI passes, I think this is ready to merge. :)