Introduce a normalization chapter

Author: BoxyUwU

src/SUMMARY.md

@@ -156,6 +156,7 @@
     - [ADTs and Generic Arguments](./ty_module/generic_arguments.md)
     - [Parameter types/consts/regions](./ty_module/param_ty_const_regions.md)
 - [`TypeFolder` and `TypeFoldable`](./ty-fold.md)
+- [Aliases and Normalization](./normalization.md)
 - [Typing/Param Envs](./typing_parameter_envs.md)
 - [Type inference](./type-inference.md)
 - [Trait solving](./traits/resolution.md)
@@ -175,7 +176,6 @@
         - [Coinduction](./solve/coinduction.md)
         - [Caching](./solve/caching.md)
         - [Proof trees](./solve/proof-trees.md)
-        - [Normalization](./solve/normalization.md)
         - [Opaque types](./solve/opaque-types.md)
         - [Significant changes and quirks](./solve/significant-changes.md)
     - [`Unsize` and `CoerceUnsized` traits](./traits/unsize.md)