reflect: stable type path v2

[soqb]

Objective

• Introduce a stable alternative to std::any::type_name.
• Rewrite of stable reflect type name #5805 with heavy inspiration in design.
• On the path to bevy_reflect: Type aliases #5830.
• Part of solving Reflect: Allow to override the type name #3327.

Solution

• Add a TypePath trait for static stable type path/name information.
• Add a TypePath derive macro.
• Add a impl_type_path macro for implementing internal and foreign types in bevy_reflect.

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Changelog

• Added TypePath trait.
• Added DynamicTypePath trait and get_type_path method to Reflect.
• Added a TypePath derive macro.
• Added a bevy_reflect::impl_type_path for implementing TypePath on internal and foreign types in bevy_reflect.
• Changed bevy_reflect::utility::(Non)GenericTypeInfoCell to (Non)GenericTypedCell<T> which allows us to be generic over both TypeInfo and TypePath.
• TypePath is now a supertrait of Asset, Material and Material2d.
• impl_reflect_struct needs a #[type_path = "..."] attribute to be specified.
• impl_reflect_value needs to either specify path starting with a double colon (::core::option::Option) or an in my_crate::foo declaration.
• Added bevy_reflect_derive::ReflectTypePath.
• Most uses of Ident in bevy_reflect_derive changed to use ReflectTypePath.

Migration Guide

• Implementors of Asset, Material and Material2d now also need to derive TypePath.
• Manual implementors of Reflect will need to implement the new get_type_path method.

Open Questions

• This PR currently does not migrate any usages of std::any::type_name to use bevy_reflect::TypePath to ease the review process. Should it? Migration will be left to a follow-up PR.
• This PR adds a lot of #[derive(TypePath)] and T: TypePath to satisfy new bounds, mostly when deriving TypeUuid. Should we make TypePath a supertrait of TypeUuid? Should we remove TypeUuid in favour of TypePath?