Improve documentation and tests on crates features

[mockersf]

How can Bevy's documentation be improved?

Bevy internal crates exposes many features, it can be hard to know which are often useful together for crate consumers. Those features and sets should be documented and tested in CI

• Document features in individual crates like they are on the top level Bevy crate
• Add feature collections for individual crates
• Add a command to CI script that will try to compile feature collections of a given crate / all crates