Updated World, UnsafeWorldCell Resource methods to use Res, ResMut

[bushrat011899]

Objective

• Fixes World::resource and allies do not return Res / ResMut smart pointers #9926

Solution

• Updated UnsafeWorldCell Resource methods to return either Res or ResMut where appropriate, using get_resource_with_ticks to obtain the relevant data.
• Updated associated methods in World
• Cascaded changes across Bevy as required.

---

Changelog

• Updated UnsafeWorldCell::get_resource(_mut) to return Res/ResMut
• Updated World::(get_)resource(_mut) to return Res/ResMut
• Updated World::resource_scope to use ResMut

Migration Guide

Simply use into_inner() to retrieve the inner reference for &R being replaced with Res, and into for Mut and ResMut.

[joseph-gio]

I don't see much reason to change Mut<> to ResMut<>. They do the same thing -- the only reason that ResMut exists is because with SystemParam, you have to distinguish between components and resources via the type itself. Here, we're able to use the method's name to distinguish between components and resources, making ResMut unnecessary. We already treat Mut as the "canonical" change detection smart pointer: ResMut::reborrow returns Mut, for example.

[bushrat011899]

the only reason that ResMut exists is because with SystemParam [...] We already treat Mut as the "canonical" change detection smart pointer: ResMut::reborrow returns Mut, for example.

Between that, and this comment from @cart, I'm going to switch this PR to draft and make some fairly major changes.

[joseph-gio]

Going to close this out since we're likely going to move in the direction described in #11825