Avoid using "data type" to mean just "type".

The term "data type" is rare in the book to begin with.  I've left a
couple places where it refers to a type that stores some kind of data.
But in most places (as pointed out by Kyle during review of this PR)
we're talking about both types that do and don't have storage.

Author: amartini51

Sources/TSPL/TSPL.docc/LanguageGuide/ClassesAndStructures.md

@@ -53,7 +53,7 @@ come at the cost of increased complexity.
 As a general guideline,
 prefer structures because they're easier to reason about,
 and use classes when they're appropriate or necessary.
-In practice, this means most of the custom data types you define
+In practice, this means most of the custom types you define
 will be structures and enumerations.
 For a more detailed comparison,
 see [Choosing Between Structures and Classes](https://developer.apple.com/documentation/swift/choosing_between_structures_and_classes).

Sources/TSPL/TSPL.docc/LanguageGuide/NestedTypes.md

@@ -1,6 +1,6 @@
 # Nested Types
 
-Define data types inside the scope of another data type.
+Define types inside the scope of another type.
 
 Enumerations are often created to support a specific class or structure's functionality.
 Similarly, it can be convenient to define utility classes and structures

Sources/TSPL/TSPL.docc/LanguageGuide/Properties.md

@@ -1549,7 +1549,7 @@ the property wrapper exposes only one piece of information ---
 whether the number was adjusted ---
 so it exposes that Boolean value as its projected value.
 A wrapper that needs to expose more information
-can return an instance of some other data type,
+can return an instance of some other type,
 or it can return `self`
 to expose the instance of the wrapper as its projected value.