Adjust abstracts

[amartini51]

Fixes rdar://102988487
Fixes rdar://102988514
Fixes rdar://102995541
Fixes rdar://103188927

[krilnon]

Seems like a reasonable change. If I had to gripe, it'd be that you can nest types inside of other types regardless of whether they're specifically data types.

[amartini51]

you can nest types inside of other types regardless of whether they're specifically data types

Oh, interesting — I think I treat "type" and "data type" as synonyms. Would a non-data type be something like an enum with no cases, used to create a pseudo-namespace?

Looking at usage within TSPL, "data types" is actually pretty rare, so it might be worth changing those to just "types" to be more consistent:

% git grep 'data type'
LanguageGuide/AdvancedOperators.md:You can use bit shifting to encode and decode values within other data types:
LanguageGuide/ClassesAndStructures.md:In practice, this means most of the custom data types you define
LanguageGuide/NestedTypes.md:Define one data type inside of another data type.
LanguageGuide/Properties.md:can return an instance of some other data type,

[krilnon]

Would a non-data type be something like an enum with no cases, used to create a pseudo-namespace?

Yeah, or any type that doesn't have storage requirements, like a protocol that defined methods and accessor functions. In contrast to something like a Point, where most of the purpose of the type is to store data.

[amartini51]

@krilnon I've changed "data type" here and in a couple other places in e19bb77.