Include shared docs in both trait and derive documentation

I think it would make sense to split out the derive syntax section of the `Component` and `Event` docs into a separate markdown file, then `#[doc = include_str!("…")]` it in both the trait doc and the derive macro doc.

_Originally posted by @SpecificProtagonist in https://github.com/bevyengine/bevy/issues/19523#issuecomment-2953728453_

Locate the `Component` and `Event` trait documentation and their derive macro documentation, then identify the derive syntax section shared between them. Extract that section into a markdown file and include it in both documentation locations; done means both docs contain the same shared derive syntax content.

Written by the indexing model from the issue text.