Move the `RichXYZ` classes out of the `runtime` package

[dwijnand]

In my opinion the RichXYZ classes should be moved outside of the runtime package. The runtime package is not supposed to be part of the public API.

Originally posted by @sjrd in #2086 (comment)

[SethTisue]

@sjrd where would they go instead?

[sjrd]

Probably the companions of their corresponding primitives.