Refactor array types to consider the length a const argument

Author: BoxyUwU

src/types/array.md

@@ -3,15 +3,15 @@ r[type.array]
 
 r[type.array.syntax]
 ```grammar,types
-ArrayType -> `[` Type `;` Expression `]`
+ArrayType -> `[` Type `;` GenericArgsConst `]`
 ```
 
 r[type.array.intro]
 An array is a fixed-size sequence of `N` elements of type `T`. The array type
 is written as `[T; N]`.
 
 r[type.array.constraint]
-The size is a [constant expression] that evaluates to a [`usize`].
+The size is a [const argument] of type [`usize`].
 
 Examples:
 
@@ -32,3 +32,4 @@ always bounds-checked in safe methods and operators.
 
 [`usize`]: numeric.md#machine-dependent-integer-types
 [constant expression]: ../const_eval.md#constant-expressions
+[const argument]: ../items/generics.md##const-generics