Update Style Guide to suggest TitleCase for Type aliases as is the reality in the standard library

[Zirunis]

closes #25859

As @taylordotfish noticed the standard library seems to treat type aliases as types and uses TitleCase. I have changed the relevant parts in the style guide accordingly.

I have also taken the liberty of improving the wording to make it a little simpler to parse for a human. I did this in a separate commit though so if this is unintended, only the first commit could be merged.