add test checking that types are registered (as far as possible)

[jakobhellermann]

Objective

1. every type that is used somewhere in a reflected type should be registered
2. every component/resource that is registered should include their respective ReflectResource/ReflectComponent type data

Solution

• Luckily both objectives can be checked at runtime, so add a test that does exactly that
• register the missing types

Note: this does not lint for types that implement Reflect but are not registered. This can't be done at runtime, but maybe as a script running on rustdoc output.

[jakobhellermann]

I chose to only register Option<Vec2> here. We could in theory register Option<T>, Vec<T> etc. for every conceivable type, but since there's no need to do this where the types are defined and it would introduce a lot of unnecessary TypeInfo into the binary I opted to only register those that are currently in use.

[mockersf]

seems related to #5781

[jakobhellermann]

seems related to #5781

Yes, that would make half of this PR obsolete.

[richchurcher]

Backlog cleanup: closing due to inactivity, and seemingly partially covered by the merge of #5781 earlier this year. See also #15030 with similar goals.