Fix Deploy Docs GH Action: Add feature(rustdoc_internals) to bevy_material when building docs

[kfc35]

Objective

• Add a fix for currently failing Deploy Docs Action. Example Log is here
• Happening on main since bevy_material #22426, It appears bevy_material is using #[doc(fake_variadic)] in a module, but doc builds for the crate aren’t building correctly. It suggests help: add #![feature(rustdoc_internals)] to the crate attributes to enable

Solution

• Copy some configuration into bevy_material that is already used in other bevy crates that have #[doc(fake_variadic)], e.g. bevy_math https://github.com/bevyengine/bevy/blob/main/crates/bevy_math/src/lib.rs#L2-L10 which adds the rustdoc_internals feature when building docs
• I added the icon stuff while I was at it since that seems to be in other lib.rs files as well

Testing

I did not test this, but this seems to be a solved problem already for the other crates