Accessibility by default

These are fine for now, but needing to specify accessibility components manually kind of defeats the purpose of "accessibility by default", increases the burden on individual developers, and makes our UI examples more bloated / less approachable. I don't think its reasonable to expect your average game developer to remember to do this / do it correctly. Ideally our main "ui introduction example" has no explicit accessibility components.

Definitely cool with this as an initial step, but I think its very important to resolve this in the near future.

_Originally posted by @cart in https://github.com/bevyengine/bevy/pull/6874#discussion_r1122340720_

Start by reviewing the original discussion in pull request #6874 and the main UI introduction example mentioned in the issue. Clarify how accessibility components should be provided by default; done should mean that example no longer requires explicit accessibility components while remaining correct for average game developers.

Written by the indexing model from the issue text.