Rename bevy_reflect's documentation feature to reflect_documentation

[WaterWhisperer]

Objective

Fixes #14309

Solution

Renamed the bevy_reflect feature from documentation to reflect_documentation to follow the naming convention where features are prefixed with their module name.

Changes

• Renamed feature documentation to reflect_documentation in:
  • bevy_reflect/Cargo.toml
  • bevy_reflect/derive/Cargo.toml
  • bevy_internal/Cargo.toml
• Updated all conditional compilation attributes from #[cfg(feature = "documentation")] to #[cfg(feature = "reflect_documentation")]
• Updated example documentation in reflect_docs.rs

Testing

[WaterWhisperer]

This PR renames a Cargo feature. Should this have a migration guide?

Users who explicitly enabled bevy_reflect/documentation in their Cargo.toml would need to change it to bevy_reflect/reflect_documentation. However, I'm not sure how common this use case is.

If needed, I‘ll add a migration guide.

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Please review the instructions for writing migration guides, then expand or revise the content in the migration guides directory to reflect your changes.

[alice-i-cecile]

I quite like this change but it needs a migration guide entry :)